Influence of Vegetation Coverage on Surface Runoff and Soil Moisture in Rainy Season in Dry-hot Valley

[Objective]The research aimed to study the effects of vegetation coverage on the changes of soil moisture in rainy season in dry-hot valley.[Method]The surface runoff and soil moisture of slope with vegetation coverage and bare land in rainy reason in Jinsha River at Yuanmou County of Yunnan Province were observed continuously.Moreover,the statistical analysis was made based on the observation data.[Result]The vegetation coverage could decrease surface runoff and the surface runoff on bare land（CK） was 22 times as the plot with vegetation coverage.The soil water content in 0-180 cm layer with vegetation coverage increased by 37.8% than bare land.The stability of soil moisture content in deep layer was enhanced and the physical properties stability of soil was maintained.The soil moisture content in different depth of soil had significant difference and the changes of soil moisture content were obviously different.[Conclusion]The vegetation coverage of slope could change the soil hydrology obviously and keep soil moisture at the higher level,especially at soil layer below 20 cm.

Effect of Typical Vegetation Restoration Pattern on Soil and Water Conservation in Yuanmou Dry-hot Valley of Yunnan Province

In Yuanmou dry-hot valley of Yunnan Province,three typical vegetation restoration patterns including production forest transformed from sloping fields to terracing,ecological afforestation within the gully and ecological aforestation in gully head and slope were selected to compare their effects on soil and water conservation.Soil and water loss,soil infiltration rate and the soil moisture dynamics of soil profile with the depth of 0-100 cm of these three patterns and their controls were observed by established standard observation plots in rainy season.The results showed that the soil and water loss of ecological afforestation and production forest terrace reduced by over 30% and 60% compared with their controls（without growth of any vegetation）respectively,showing significant control effect on the soil and water loss.Vegetation restoration also apparently increased the infiltration rate of soil（increased by 100%-200%）.In rainy season,the soil moisture content of ecological afforestation and production forest terrace increased by over 30% and 100% compared with their controls.This indicated that vegetation restoration will not lead to soil aridity during the rainy season;vegetation restoration not only reduced the loss of surface water and soil fine particles,but also enhanced the infiltration of precipitation.These two effects made the soil moisture content increase throughout the profile.

The dry-hot valleys and forestation in southwest china

The dry-hot valleys (DHV) are located mainly in the deeply incised v alleys along the upper streams of several international and domestically rivers, like Yangtz, Zhu, Lanchang, Hong, and Nu rivers. This paper briefly described t he reasons of formation of DHV from view of climate and geographical conditions, and by referring to great deal of documents, analyzed the historical case and p resent status of the vegetations in DHV. The environment in DHV is facing the se rious vulnerable period in the history due to its nature situation of half-year dry period, fragile geological structure and shallow soil, and its social situat ion of over dense population and over farming. The primary vegetation is broad l eaf forest and it was denuded in the history. The current local vegetation is th e degraded secondary vegetation: savanna and succulent thorny shrub. Since the e nvironmental situation in valley influenced directly the water body of river, th e soil erosion control and re-vegetation in DHV is the most urgent task in the p rocess of environmental harness along the rivers. Quite a few pilot research pro jects have been carried out.on demonstrating new silviculture techniques for re- vegetation in DHV, but there still exist great difficulties in carrying out larg e-scale afforestation engineering.

Livelihood Strategy and Farmland Use in Xinping County of Yuanjiang Dry-hot Valley

Methods of participatory rural appraisal and mathematical statistics were adopted to study livelihood diversification, livelihood strategy and farmland use of the four types of farmers in Xinping County of Yuanjiang dry-hot valley with field survey data. The results showed as follows： firstly, as farmers are transforming from pure agriculture to non-agriculture, their agricultural livelihood diversification index will decrease, while non-agricultural livelihood diversification index will increase. In term of livelihood activities, pure agricultural farmers are exclusively engaged in agricultural activities, agricultural-dominant and non-agricultural-dominant farmers are engaged in both agricultural and non-agricultural ones, while non-agricultural farmers are basically engaged in off-farm activities. Secondly, as for crops planted, pure agricultural and agricultural-dominant farmers tend to choose those crops with more investment,shorter growth period and higher value, meanwhile non-agricultural-dominant farmers tend to choose crops with less investment, simpler management and longer growth period. Thirdly, to cope with current problems in farming, pure agricultural farmers will adopt measures such as changing planting structure, maintaining or expanding planting scale, increasing planting investment and renting in more land to promote the development of farming; agriculture-dominant farmers will adopt measures such as changing planting structure, reducing planting scale, maintaining planting investment, renting in and taking back the leased land as well as engaging in non-agricultural activities to overcome the difficulties faced; while non-agricultural-dominant farmers will adopt measures such as reducing both planting scale and investment,changing planting structure and engaging in farmland transfer as well as various offfarm activities to avoid livelihood risks.

Simulation of Morphological Development of Soil Cracks in Yuanmou Dry-hot Valley Region, Southwest China

Soil cracking is an important process influencing water and solutes transport in the Yuanmou Dry-hot Valley region of Southwest China. Studying the morphological development of soil cracks helps to further reveal the close relationship between the soil cracking process and water movement in such semi-arid regions. Here we report regular changes on surface morphology of soil cracks with decreasing water in four different soils (Typ-Ustic Ferrisols,Ver-Ustic Ferrisols,Tru-Ustic Vertisols and Typ-Ustic Vertisols) through simulation experiments. Our results indicate the following: 1) Different soils ultimately have different development degrees of soil cracks,according to their various values of crack area density. Soil cracks in Typ-Ustic Ferrisols can only develop to the feeble degree,while those in the other three soils are capable of developing into the intensive degree,and even into the extremely intensive degree. 2) Soil crack complexity,as expressed by the value of the area-weighted mean of crack fractal dimension (AWMFRAC),is found to continuously decrease as a whole through the whole cracking process in all the studied soils. 3) Soil crack connectivity shows a uniform trend in the studied soils,that is to say,connectivity gradually increases with soil crack development.

Responses of Dodonaea viscosa growth and soil biological properties to nitrogen and phosphorus additions in Yuanmou dry-hot valley

Nitrogen(N) and phosphorus(P) are limited nutrients in terrestrial ecosystems, and their limitation patterns are being changed by the increase in N deposition. However, little information concerns the plant growth and the soil biological responses to N and P additions among different soils simultaneously, and these responses may contribute to understand plant-soil interaction and predict plant performance under global change. Thus, this study aimed to explore how N and P limitation changes in different soil types, and reveal the relationship between plant and soil biological responses to nutrient additions. We planted Dodonaea viscosa, a globally distributed species in three soil types(Lixisols, Regosols and Luvisols) in Yuanmou dry-hot valley in Southwest China and fertilized them factorially with N and P. The growth and biomass characters of D. viscosa, soil organic matter, available N, P contents and soil carbon(C), N, P-related enzyme activities were quantified. N addition promoted the growth and leaf N concentration of D. viscosa in Lixisols; N limitation in Lixisols was demonstrated by lower soil available N with higher urease activity. P addition promoted the growth and leaf P concentration of D. viscosa in Luvisols; severe P limitation in Luvisols was demonstrated by a higher soil available N: P ratio with higher phosphatase activity. Urease activity was negatively correlated with soil available N in Nlimited Lixisols, and phosphatase activity was negatively correlated with soil available P in P-limited Luvisols. Besides, the aboveground biomass and leaf N concentration of D. viscosa were positively correlated with soil available N in Lixisols, but the aboveground biomass was negatively correlated with soil available P. Our results show similar nutrient limitation patterns between plant and soil microorganism in the condition of enough C, and the nutrient limitations differ across soil types. With the continued N deposition, N limitation of the Lixisols in dry hot valleys is expected to be alleviated, while P limitation of the Luvisols in the mountaintop may be worse in the future, which should be considered when restoring vegetation.

Sap flow characteristics of three afforestation species during the wet and dry seasons in a dry-hot valley in Southwest China

Assessing and using tree species （exotic or native） with superior tolerance to environmental stresses （such as drought and high temperature） play an important role in afforestation practices. In the present study, stem sap flow characteristics and responses to ambient meteo- rological factors of three tree species, Albizzia kalkora （native）, Azadirachta indica （exotic）, and Acacia auriculaeformis （exotic）, in a dry-hot valley （Yuanmou, Yunnan Province, China） were investigated using thermal dissipation probes. The diurnal dynamics of sap flow in three studied species displayed an obvious circadian rhythm during the wet and dry seasons, with the exception of A. indica during the dry season. The sap flow velocity （SFV） in A. kalkora and A. auriculaeformis was significantly positively correlated with photosynthetically active radiation （PAR）, air temperature, vapour pressure deficit （VPD） and wind speed, but negatively correlated with atmospheric relative humidity over the two seasons. The cross-corre- lation analysis also revealed that the SFV of the three species was significantly correlated with PAR and VPD （P 〈 0.001）. Additionally, stem sap flow lagged behind PAR but ahead of VPD, and the diurnal sap flow was more dependent on PAR than on VPD. However, we found that the dominant climatic factor influencing the stem sap flow differed between daytime and nighttime. PAR was more influential than other meteorological factors during the daytime, while VPD or other factors were more influential overnight. When the nighttime refilling ability of the three tree species was compared, our results suggest that A. indica has higher drought resistance and better for afforestation of the studied region.

Anthropogenic Impacts on the Sediment Flux in the Dry-hot Valleys of Southwest China—an Example of the Longchuan River

The sediment flux data, measured from a dry-hot valley of the Longchuan River, a tributary of the lower Jinsha River, were analyzed with Mann-Kendall test, Seasonal Mann-Kendall test and Sen’s test. In both the upper reaches (Xiaohekou) and the lower reaches (Xiaohuangguayuan), the sediment fluxes showed a significant increase from 1970 to 2001, despite the fact that the water discharge did not change significantly during the period and numerous reservoir constructions which contribute to the trap of sediment. This can be attributed to the intensification of human activities, especially the activities related to land surface disturbances such as deforestation and afforestation, expansion of agriculture land, and road constructions. This increase is more significant in the lower reaches of the river observed at the place of Xiaohuangguayuan due to the dry-hot climate. The profound increase in sediment flux has significant implications for effective management of the sedimentation problems of the on-going Three Gorges Reservoir.

Effects of vegetation coverage and seasonal change on soil microbial biomass and community structure in the dry-hot valley region

Soil microorganisms are sensitive indicator of soil health and quality. Understanding the effects of vegetation biomass and seasonal change on soil microorganisms is vital to evaluate the soil quality and implement vegetation restoration. This study analyzed the soil phospholipid fatty acids(PLFAs) in fresh and withered Kudzu(Pueraria montana var. lobata) vegetation conditions in different seasons. The results showed that vegetation biomass and seasonal change significantly affected microbial biomass and its community structure. Both fresh and withered Kudzu cover significantly increased soil microbial biomass, and the growth effect of microbes in the soil with fresh Kudzu cover was more obvious than that with withered Kudzu cover. Compared with the dry season, the rainy season significantly increased the microbial biomass and the B/F(the ratio of bacterial to fungal PLFAs) ratio but dramatically reduced the G+/G-(the ratio of gram-positive to gram-negative bacteria PLFAs). Kudzu cover and seasonal change had a significant effect on microbial structure in soil covered by higher vegetation biomass. Furthermore, soil temperature and moisture had different correlations with specific microbial biomass in the two seasons. Our findings highlight the effect of Kudzu vine cover on the soil microenvironment and soil microhabitat, enhancing the soil quality in the Dry-hot Valley of Jinsha River, Southwest China.

Morphology and controlling factors of the longitudinal profile of gullies in the Yuanmou dry-hot valley

The morphology of the gully longitudinal profile （GLP） is an important topographic index of the gully bottom associated with the evolution of the gullies. This index can be used to predict the development trend and evaluate the eroded volumes and soil losses by gullying. To depict the morphology of GLP and understand its controlling factors, the Global Positioning System Real-time Kinematic （GPS RTK） and the total station were used to measure the detail points along the gully bottom of 122 gullies at six sites of the Yuanmou dry-hot Valley. Then, nine parameters including length （Lt）, horizontal distance （Dh）, height （H）, vertical erosional area （A）, vertical curvature （Co）, concavity （Ca）, average gradient （Ga）, gully length-gradient index （GL）, normalized gully length-gradient index （Ngl）, were calculated and mapped using CASS, Excel and SPSS. The results showed that this study area is dominated by slightly concave and medium gradient GLPs, and the lithology of most gullies is sandstone and siltstone. Although different types of GLPs appear at different sites, all parameters present a positively skewed distribution. There are relatively strong correlations between several parameters： namely Lt and H, Dh and H, Lt and A, Dh and A, H and GL. Most GLPs, except three, have a best fit of exponential functions with quasi- straight shapes. Soil properties, vegetation coverage, piping erosion and topography are important factors to affect the GLP morphology. This study provides useful insight into the knowledge of GLP morphology and its influential factors that are of critical importance to prevent and control gully erosion.

A novel model to assess soil productivity in the dry-hot valleys of China

Accurate evaluation of soil productivity has been a long-standing challenge. Although numerous models for productivity assessment exist, most are cumbersome to use and require substantial parameter inputs. We developed a new empirical soil productivity model based on field investigations of soil erosion, soil physieoehemieal properties, and crop yields in the dry-hot valleys （DHVs） in China. We found that soil pH, and organic matter and available potassium contents significantly affected crop yields under eroded conditions of the DHVs. Moreover, available potassium content was the key factor affecting soil productivity. We then modified an existing soil productivity model by adding the following parameters： contents of effective water, potassium, organic matter, and clay, soil pH, and root weighting factor. The modified soil productivity model explained 63.5% of the crop yield. We concluded that the new model was simple, realistic, and exhibited strong predictability. In addition to providing an accurate assessment of soil productivity,our model could potentially be applied as a soil module in comprehensive crop models.

The morphological characteristics of gully systems and watersheds in Dry-Hot Valley, SW China

Gully systems and watersheds are geomorphic units with clear boundaries that are relatively independent of basin landscapes and play an important role in natural geography. In order to explore the morphological characteristics of gully systems and watersheds in the Dry-Hot Valley [South West(SW) China], gullies are interpreted from online Google images with high resolution and watersheds are extracted from digital elevation model at a scale of 1:50,000. The results show that:(1) There are17,382 gullies(with a total area of 1141.66 km2) and 42 watersheds in the study area.(2) The average gully density of the study area(D) is 4.29 km/km2, gully frequency(F) is 14.39 gullies/km2, the branching ratio(B) is 5.13, the length ratio(L) is 3.12, and the coefficient of the main and tributary gullies(M) is 0.06. The degree of gully erosion isstrong to extremely strong, the main development intensity of gully erosion ranges from intense to moderate, and the type of gully system is tributary.(3) The watershed areas(A) are between 0.39 and 96.43 km2, the relief ratio(R) is from 0.10 to 0.19, the circularity ratio(C) is from 0.30 to0.83, the texture ratio(T) is from 0.82 to 39.35, and the dominant geomorphological texture type is fine.(4) There is a quantitative relationship between F and D:F = 0.624 D2(R =0.84) and T is closely related to D, F, M(R2[ 0.7). A,R and C are related to M(R2[ 0.5). The development of gully systems is the result of coupling effects between multiple factors. In this area, the degree of erosion and the condition of the main and tributary gullies can be controlled by the degree of topographic breakage in the watershed, which provides some theoretical basis for the evaluation of gully erosion by the latter. In addition, the scale, relief, and shape have a significant impact on the locations of the main and tributary gullies. For tributary gullies, attention should be paid to the interception and control of runoff and sediment in the small confluence branches in order to prevent gully expansion and head advance. These features can inform the development of targeted measures for the control of soil erosion.

Effects of Land Use Change on the Ecosystem Services Value in the Dry-Hot Valley

The objective of the study reported here was to determine whether LANDSAT TM images could be used to quantify changes in land-use and ecosystem services in Yuanmou County. The sizes of six land use/land cover （LUCC） categories were estimated in Yuanmou County according to the LANDSAT TM images in the summer of 1986 and 2005. Coefficients published by Xie Gaodi and co-workers in 2003 were used to value changes in ecosystem services delivered by each land use/land cover category, and the ecosystem services sensitivity analysis was conducted to determine the effect of manipulating these coefficients on the estimated values. The important results are summarized as followings. （1） The estimated size of cultivated land, pasture land, water area and unused land decreased by 6.39%, 1.35%, 2.25% and 10.67% respectively between 1986 and 2005. By contrast, the estimated size of forest land and construction land increased by about 2.23% and 71.15% respectively between 1986 and 2005. （2） The total ecosystem services value （EVS） of the study area increased from 2 142 132 609.46 yuan to 2 146 416 621.00 yuan, with the net increase of 4 284 011.54 yuan during the 20-year time period. （3） The coefficient sensitivity （CS） of the study are less than unity in all cases （CS 〈 1）. This indicates that the total ecosystem values estimated for the study area are relatively inelastic with respect to the ecosystem service coefficients. While this implies that our estimates are robust and the coefficient is reasonable, highly under or over valued coefficients can substantially affect the veracity of estimated changes in ecosystem service values overtime even when the CS are less than unity（CS 〈 1）.

Planar morphology and controlling factors of the gullies in the Yuanmou Dry-hot Valley based on field investigation

The plane form of a gully can provide a basis for evaluating the gully volume and erosion rate, acting process, and evolutionary stage. For describing the planar characteristics of a permanent gully and understanding their controlling factors, this study, utilizing a total station and GPS RTK, measured the shoulder lines and channel curves of 112 gullies in six sites of the Yuanmou Dry-hot Valley and then mapped them by Arc GIS software and calculated nine parameters. The results showed that the channel lengths range from 10.88 to 249.11 m; the widths range from 6.20 to 40.99 m; the perimeters range from 54.11 to 541.67 m; the gully areas range from 153.02 to 6,930.30 m2; the left-side areas range from 92.93 to 4,027.20 m2; and the right-side areas range from 63.65 to 3,539.77 m2. The slightly sinuous and straight gullies account for 73.21% of the total gullies; the quantity of the right skewed gullies is 8.93% greater than that of the left skewed ones based on the symmetry ratio; the shape ratios range from 1.12 to 1.40 and the morphology ratios from 0.038 to 1.294; the fractal dimension is 1.192. Gullies in different sites have diverse planar characteristics. Except for the symmetry index, which was close to a negatively skewed distribution, all of the other parameters had the characteristic of positively skewed distribution. The gully area is related to the length and width, but the gully length has a weak correlation with the width. The evolutionary stage, topographic conditions, strata, soil properties, and piping erosion played very important roles in the gully planar morphology. This study could provide useful information for controlling gully erosion and safeguarding human habitation and engineering buildings.

Industrial Poverty Alleviation Model in Deep Poverty-stricken Villages in the Dry-hot Valley of Jinsha River: A Case Study of Poverty Alleviation in the Green Prickleyash Planting Industry in Laopingzi Village,Luquan County

Industrial poverty alleviation is the core of poverty alleviation in rural areas of China,and it is the fundamental way for the rural poor to achieve stable income and poverty alleviation. Laopingzi Village,Jiaopingdu Town,Luquan County,Kunming County,Yunnan Province,located in the dry-hot valley area of Jinsha River,has become a typical deep poverty-stricken village due to its special natural conditions.In recent years,in the battle to win the fight against poverty,the people of Laopingzi Village have achieved a virtuous cycle of the ecological environment and an access to get rid of poverty and get rich through vigorously developing green prickleyash planting industry. By the end of 2018,the incidence of poverty in Laopingzi Village Committee dropped from 45. 62% in 2014 to 1. 11%,and the green prickleyash planting industry had achieved remarkable results in poverty alleviation. This article summarizes the specific practices of developing the green prickleyash planting industry in the village,analyzes the main results and successful experiences of the mode and discusses the inspiration of the implementation of green prickleyash cultivation on industrial poverty alleviation,so as to provide an effective practical example for the development and poverty alleviation of poverty-stricken areas.

Poverty Alleviation Mode by Developing Sorghum Planting Industry in Dry-hot Valley Areas of Jinsha River in China:Taking Luquan Yi and Miao Autonomous County of Yunnan Province as an Example

There are many state-level poverty-stricken counties in the dry-hot valley areas of Jinsha River in China,with a wide range of poverty and extreme degree of poverty.The industry-supporting poverty alleviation ranks first in the"five batches"of China's targeted poverty alleviation strategy.The practice of planting in Luquan County since 2017 shows that the valleys and slopes on the dry-hot valley areas of Jinsha River with an altitude above 1800 m have wide land suitable for sorghum planting,and suitable for introduction and planting.In recent years,the county has adopted the mode of enterprise+government+cooperative+poor household,introduced the Langzhitang wine factory,developed sorghum planting with large-scale,industrialized and specialized features to achieve stable income growth for the poor,and significant results have been achieved.Based on many field surveys,household surveys,and interviews with county and village leaders,this paper analyzes the specific practices and main effects of the county's poverty alleviation model by developing sorghum planting industry,aiming to provide necessary reference for the targeted poverty alleviation and poverty alleviation in similar areas of Yunnan Province and other provinces.

Seasonal Dynamics of the Soil Moisture in Yuanmou Dry-Hot Valley of Yunnan

[ Objective] The research aimed to study seasonal dynamics of the soil moisture in Yuanmou Dry-Hot Valley of Yunnan. [ Method] We investigated soil moisture in rainy season in Yuanmou Dry-Hot Valley. By combining completed research about soil moisture in dry season, data in rainy and dry seasons were contrasted to study seasonal dynamics of the soil moisture in the zone. [ Resultl Soil moisture in rainy season increased with the depth of soil, but would decrease within 1.0 m below the root layer. The soil moisture of grassland was higher than that of the woodland, while soil moisture of the savanna was higher than that of the woodland but lower than that of the grassland. In addition, compared with soil mois- ture in dry season, it is clear that to avoid forming permanent soil desiccation, based on soil and hydrology conditions in Yuanmou, it is better to plant grass not tree in Yuanmou when we do something about ecological restoration. [ Condusion] The research had certain guidance significance for planting agricultural and economic crops and carrying out ecological restoration in Yuanmou Dry-Hot Valley.

Livelihood Capital and Livelihood Diversification for Different Farmers in Yuanjiang Dry-Hot River Valley

Under the analytical framework of sustainable livelihoods,we establish the evaluation indicator system for farmers' livelihood capital,to evaluate the current livelihood capital and livelihood diversification for different farmers in the Dai nationality region of Xinping County in the Yuanjiang dry-hot river valley area,and discuss the relationship between livelihood capital and livelihood diversification. Studies have shown that the mode dominated by agriculture,supplemented by non-agricultural activities,combined with breeding,is the commonly used livelihood strategy for farmers in this region. As farmers change from pure agriculture to non-agriculture,their total livelihood capital and nonagricultural livelihood diversification index will increase,while agricultural livelihood diversification index will decrease. In the meantime,their livelihood activities gradually shift from agricultural to non-agricultural ones,which is mainly reflected in the combination of both agricultural and non-agricultural activities. Regression analysis on livelihood capital and livelihood diversification shows that natural and physical capital is the basis of realizing agricultural livelihood diversification. Farmers with rich natural and physical capital will prefer agricultural livelihood strategies. While financial and human capital is the driving force for farmers' transition from pure agriculture to non-agriculture.

IMPACT OF WATER ENVIRONMENTAL CHARACTERISTICS IN DRY-HOT VALLEY OF JINSHA RIVER ON SOIL DESERTIFICATION

Based on the field investigation and the analysis of soil moisture curve, it is clearly shown that there is a positive relationship between vegetation coverage rate and soil moisture capacity and soil depth in dry hot valley of the Jinsha River, and also there is a desertification process with seasonality. It is suggested that the basic factor of desertification in the area is water deficiency (seasonal drought and low soil water capacity) and the direct dynamic of desertification is soil erosion. Some effective countermeasures are presented, of which water saving planting and irrigation techniques should be firstly applied in the studied area.

苹果丁冷冻-热风联合干燥体积收缩机制

为降低冻干苹果能耗,同时获得具有良好外观的脱水产品,该研究将冷冻-热风联合干燥应用于苹果脱水加工,并从水分迁移角度探究此过程中产品的收缩机制。选取4个水分转换点(干基含水率分别为1.00、0.76、0.53和0.33 g/g)对苹果进行联合干燥处理,并对脱水产品的收缩率、质构特性、微观结构、孔隙分布及样品在热风干燥阶段的水分迁移与分布进行测定及分析。结果表明,联合干燥样品的收缩情况显著(P<0.05)优于单一热风干燥样品,且转换点对样品收缩率影响较大(收缩率6%~45%),当转换点干基含水率低于0.53 g/g时,联合干燥样品没有出现明显的体积收缩现象。随着转换点干基含水率的升高,样品的收缩程度增大,并出现不同程度的中心塌陷,且孔隙率逐渐减小,但相应能耗降低。产品收缩主要发生在热风干燥过程的升速阶段,在此阶段样品自由水含量大幅减少,结合水与不易流动水未发生明显改变,样品内部水分在湿度差的作用下向表面迁移,这是导致联合干燥样品发生体积收缩的关键机制。该研究结果可为冷冻-热风联合干燥高效生产良好外观的脱水苹果提供数据支撑及理论参考。