Changes in the relationship between species richness and belowground biomass among grassland types and along environmental gradients in Xinjiang, Northwest China

The association between biodiversity and belowground biomass(BGB) remains a central debate in ecology.In this study, we compared the variations in species richness(SR) and BGB as well as their interaction in the top(0–20 cm), middle(20–50 cm) and deep(50–100 cm) soil depths among 8 grassland types(lowland meadow, temperate desert, temperate desert steppe, temperate steppe desert, temperate steppe, temperate meadow steppe, mountain meadow and alpine steppe) and along environmental gradients(elevation, energy condition(annual mean temperature(AMT) and potential evapotranspiration(PET)), and mean annual precipitation(MAP)) based on a 2011–2013 survey of 379 sites in Xinjiang, Northwest China.The SR and BGB varied among the grassland types.The alpine steppe had a medium level of SR but the highest BGB in the top soil depth, whereas the lowland meadow had the lowest SR but the highest BGB in the middle and deep soil depths.The SR and BGB in the different soil depths were tightly associated with elevation, MAP and energy condition;however, the particular forms of trends in SR and BGB depended on environmental factors and soil depths.The relationship between SR and BGB was unimodal in the top soil depth, but SR was positively related with BGB in the middle soil depth.Although elevation, MAP, energy condition and SR had significant effects on BGB, the variations in BGB in the top soil depth were mostly determined by elevation, and those in the middle and deep soil depths were mainly affected by energy condition.These findings highlight the importance of environmental factors in the regulations of SR and BGB as well as their interaction in the grasslands in Xinjiang.

Effects of soil nutrients and climate factors on belowground biomass in an alpine meadow in the source region of the Yangtze-Yellow rivers, Tibetan Plateau of China

Improving our knowledge of the effects of environmental factors(e.g.soil conditions,precipitation and temperature) on belowground biomass in an alpine grassland is essential for understanding the consequences of carbon storage in this biome.The object of this study is to investigate the relative importance of soil nutrients and climate factors on belowground biomass in an alpine meadow in the source region of the Yangtze and Yellow rivers,Tibetan Plateau.Soil organic carbon(SOC),total nitrogen(TN) and total phosphorous(TP) contents and belowground biomass were measured at 22 sampling sites across an alpine meadow on the Tibetan Plateau.We analyzed the data by using the redundancy analysis to determine the main environmental factors affecting the belowground biomass and the contribution of each factor.The results showed that SOC,TN and TP were the main factors that influenced belowground biomass,and the contribution of SOC,TN and TP on biomass was in the range of 47.87%–72.06% at soil depths of 0–30 cm.Moreover,the combined contribution of annual mean temperature(AMT) and mean annual precipitation(MAP) on belowground biomass ranged from 0.92% to 4.10%.A potential mechanism for the differences in belowground biomass was caused by the variations in soil nitrogen and phosphorous,which were coupled with SOC.A significant correlation was observed between MAP and soil nutrients(SOC,TN and TP) at the soil depth of 0–10 cm(P<0.05).We concluded that precipitation is an important driving force in regulating ecosystem functioning as reflected in variations of soil nutrients(SOC,TN and TP) and dynamics of belowground biomass in alpine grassland ecosystems.

Patterns of above-and belowground biomass allocation in China's grasslands:Evidence from individual-level observations

Above-and belowground biomass allocation not only influences growth of individual plants,but also influences vegetation structures and functions,and consequently impacts soil carbon input as well as terrestrial ecosystem carbon cycling.However,due to sampling difficulties,a considerable amount of uncertainty remains about the root:shoot ratio(R/S),a key parameter for models of terrestrial ecosystem carbon cycling.We investigated biomass allocation patterns across a broad spatial scale.We collected data on individual plant biomass and systematically sampled along a transect across the temperate grasslands in Inner Mongolia as well as in the alpine grasslands on the Tibetan Plateau.Our results indicated that the median of R/S for herbaceous species was 0.78 in China's grasslands as a whole.R/S was significantly higher in temperate grasslands than in alpine grasslands(0.84 vs.0.65).The slope of the allometric relationship between above-and belowground biomass was steeper for temperate grasslands than for alpine.Our results did not support the hypothesis that aboveground biomass scales isometrically with belowground biomass.The R/S in China's grasslands was not significantly correlated with mean annual temperature(MAT) or mean annual precipitation(MAP).Moreover,comparisons of our results with previous findings indicated a large difference between R/S data from individual plants and communities.This might be mainly caused by the underestimation of R/S at the individual level as a result of an inevitable loss of fine roots and the overestimation of R/S in community-level surveys due to grazing and difficulties in identifying dead roots.Our findings suggest that root biomass in grasslands tended to have been overestimated in previous reports of R/S.

Above-and belowground biomass in relation to envi- ronmental factors in temperate grasslands, Inner Mongolia

Above- and belowground biomasses of grasslands are important parameters for characterizing re- gional and global carbon cycles in grassland ecosystems. Compared with the relatively detailed in- formation for aboveground biomass (AGB), belowground biomass (BGB) is poorly reported at the re- gional scales. The present study, based on a total of 113 sampling sites in temperate grassland of the Inner Mongolia, investigated regional distribution patterns of AGB, BGB, vertical distribution of roots, and their relationships with environmental factors. AGB and BGB increased from the southwest to the northeast of the study region. The largest biomass occurred in meadow steppe, with mean AGB and BGB of 196.7 and 1385.2 g/m2, respectively; while the lowest biomass occurred in desert steppe, with an AGB of 56.6 g/m2 and a BGB of 301.0 g/m2. In addition, about 47% of root biomass was distributed in the top 10 cm soil. Further statistical analysis indicated that precipitation was the primary determinant factor in shaping these distribution patterns. Vertical distribution of roots was significantly affected by precipitation, while the effects of soil texture and grassland types were weak.

Degradation leads to dramatic decrease in topsoil but not subsoil root biomass in an alpine meadow on the Tibetan Plateau, China

Understanding the effects of degradation on belowground biomass(BGB)is essential for assessment of carbon budget of the alpine meadow ecosystem on the Tibetan Plateau,China.This ecosystem has been undergoing serious degradation owing to climate change and anthropogenic activities.This study examined the response of the vertical distribution of plant BGB to degradation and explored the underlying mechanisms in an alpine meadow on the Tibetan Plateau.A field survey was conducted in an alpine meadow with seven sequential degrees of degradation in the Zoige Plateau on the Tibetan Plateau during the peak growing season of 2018.We measured aboveground biomass(AGB),BGB,soil water content(SWC),soil bulk density(SBD),soil compaction(SCOM),soil organic carbon(SOC),soil total nitrogen(STN),soil total phosphorus(STP),soil available nitrogen(SAN),and soil available phosphorus(STP)in the 0-30 cm soil layers.Our results show that degradation dramatically decreased the BGB in the 0-10 cm soil layer(BGB0-10)but slightly increased the subsoil BGB.The main reason may be that the physical-chemical properties of surface soil were more sensitive to degradation than those of subsoil,as indicated by the remarked positive associations of the trade-off value of BGB0-10 with SWC,SCOM,SOC,STN,SAN,and STP,as well as the negative correlation between the trade-off value of BGB0-10 and SBD in the soil layer of 0-10 cm.In addition,an increase in the proportion of forbs with increasing degradation degree directly affected the BGB vertical distribution.The findings suggest that the decrease in the trade-off value of BGB0-10 in response to degradation might be an adaptive strategy for the degradation-induced drought and infertile soil conditions.This study can provide theoretical support for assessing the effects of degradation on the carbon budget and sustainable development in the alpine meadow ecosystem on the Tibetan Plateau as well as other similar ecosystems in the world.

Biomass of Natural Grassland under Different Enclosure Conditions

Taking natural grassland on the northern slope of the Qilian Mountain for example, this paper investigated and compared aboveground and belowground biomass of grassland in multi-year enclosure(20 years), one-year enclosure, control areas(natural grazing areas). The results showed that coverage and height of the enclosure sample plots were significantly higher than that of natural grazing area(P <0.05); mean aboveground biomass of grassland: multi-year enclosure(316.58 g/m^2) > one-year enclosure area(299.07 g/m^2) > multi-year enclosure control area(254.39 g/m^2) > one-year enclosure control area(187.37 g/m^2); belowground biomass: multi-year enclosure(2,906.90 g/m^2) > one-year enclosure area(2,587.26 g/m^2) > multi-year enclosure control area(2,378.93 g/m^2) > one-year enclosure control area(2,029.17 g/m^2); mean aboveground biomass of natural grassland was 263.60 g/m^2, mean belowground biomass 2,225.56 g/m^2; ratio of belowground biomass to aboveground biomass varied between 6.79 and 12.90, distribution of belowground biomass and aboveground biomass in each plot showed significant differences(P <0.05). Enclosure was favorable for improving the coverage and biomass of natural grassland plant communities in the Qilian Mountains.

Responses of biomass to the addition of water, nitrogen and phosphorus in Keerqin sandy grassland, Inner Mongolia, China

沙的草地的生产率上的水，氮和磷的效果被调查与一充分发现在东南的 Keerqin 砂土限制草地生产率的自然恢复的主要因素的因子试验。总共，八个处理作为水增加(W)被设计，氮肥增加(N)，磷化肥增加(P)，水+氮肥增加( WN )，水+磷化肥增加( WP )，氮肥+磷化肥增加( NP )，浇+氮肥+磷化肥增加( WNP )和控制( CK )。每个处理被复制六次并且随机把阴谋分到 48 (4 m × 4 m ) 那被一个 2-m 缓冲区分开。生产率的恢复被氮因素仅仅为 Keerqin 砂土并且不的沙的草地限制的结果表演走水路限制了并且磷。相对 CK 阴谋，生物资源并且未葬所有阴谋的主要生产率(ANPP ) 与氮肥增加了的网显著地被提高(P 【 0.05 ) 在 2005 生长期。草根质量在地下的生物资源是主导的。现在的学习可能低估在北中国捕捞草地的主要生产率，由于地下的生物资源大小的限制。

Effect of mixture sowing on biomass allocation in the artificially-planted pastures, Southeastern Tibetan

Artificial planting is an important measure to promote the restoration of degraded grassland and protect the ecological environment. The objectives of the current study were to investigate the allocation pattern between aboveground biomass(AGB) and belowground biomass(BGB) in different seeding types of artificially-planted pastures. We explored the variation in biomass and the relationship between above-and belowground biomass in four artificiallyplanted pastures with one species from Elymus nutans Griseb(EN, perennial), Elymus sibiricus Linn(ES, perennial), Medicago sativa Linn(MS, perennial), and Avena sativa Linn(AS, annual) and in six artificially-planted communities with mixtures of two species by seeding ratio 1:1 from the abovementioned grasses(EN + AS, MS + AS, EN + ES, MS + EN, MS + ES, AS + ES) in 2015 and 2016. The results showed that E. nutans is the most productive species with the highest biomass production among the single crops. MS + ES was the most productive group in 2015, while the group with the highest biomass production changed to AS + ES in 2016. AGB was positively correlated to BGB in the surface soil layer in the first year, but positively related to BGB in the subsoil layer in the second year. In the early stageof artificial grassland succession, plants allocated more biomass to aboveground parts, with a root to shoot(R/S) ratio of 1.98. The slope of the log-log relationship between AGB and BGB was 1.07 in 2016, which is consistent with the isometric theory. Different sowing patterns strongly affected the accumulation and allocation of biomass in artificiallyplanted grassland, E. sibiricus was the suitable plant in the alpine regions, which will be conducive to understanding vegetation restoration and plant interactions in the future.

Tree Biomass Estimation in Central African Forests Using Allometric Models

Quantifying the tropical forests’ carbon stocks is presently an important component in the implementation of the emerging carbon credit market mechanisms. This calls for appropriate allometric equations predicting biomass which currently are scarce. In this study, we aimed to estimate above- and below-ground biomass and carbon stocks of trees, and to identify the variation in diameter-height allometry of Ipendja mixed terra firme lowland tropical forest’s trees. The study area is located at Ipendja forest management unit (UFA), close to Dongou district (Likouala Department), in Northern Republic of Congo. This study combined forest inventory data of 1340 trees recorded from eight studied plots distributed in two sites, respectively Mokelimwaekili (i.e., Old-growth forest) and Sombo (i.e., Selective logging forest). Trees measurements were done with rectangular plots, each 25 × 200 m (i.e., 0.5 ha, 5000 m2). In eight studied plots (4 plots per site), only trees with DBH ≥ 10 cm were measured and identified. 1340 trees founded were belonged 145 species and 36 botanical families (n = 733 and n = 607, for Sombo and Mokelimwaekili respectively). The analyses were conducted using allometric method for aboveground biomass (AGB) and belowground biomass (BGB) estimations. The results showed that in Ipendja forest ecosystem the mean biomass is built up for AGB (346 Mg·ha-1) as well as for BGB (81.3 Mg·ha-1), with a significant difference between forest types (F = 23.46, df = 7.771, P = 0.001). It was obvious that biomasses in Mokelimwaekili (AGB: 559.7 Mg·ha-1, BGB: 131 Mg·ha-1) were higher than those of Sombo (AGB: 291.8 Mg·ha-1, BGB: 68.5 Mg·ha-1). By this study, Ipendja forest ecosystem has clearly variations on the diameter-height relationship and biomass across the plots and the sites.

Influences of various grazing systems on community biomass of a desert grassland in Inner Mongolia,China

This study investigated the effects of various grazing systems,including continuous grazing,rotational grazing,and no-grazing systems,on the community biomass in the Stipa breviflora Griseb desert grassland during the grazing seasons in 2005,2006,and 2007,based on study sites established in 1999.We found that the seasonal dynamics of the aboveground biomass were quite similar among the three treatments,which reached peak values in period from August to September during each study year.The continuous grazing system reduced the aboveground biomass from 2005 to 2007 under drought conditions,and the rotational grazing and no-grazing systems maintained more aboveground biomass than the continuous grazing system did.The belowground biomass declined with the increase of soil depth among the three treatments,and in the surface 20-cm soil layer it accounted for more than 60% of the total biomass.The belowground biomass was found to be highly correlated with soil depth under rotational grazing.The total belowground biomass within the 0-100-cm soil layer for rotational grazing was significantly higher than for continuous grazing and no-grazing,and had 15,775 kg/ha more biomass.Our results demonstrate that conservative rotational grazing can alleviate grassland deterioration by reserving more aboveground and belowground biomass than the continuous grazing system does.

Tanoak (Notholithocarpus densiflorus) Coarse Root Morphology: Prediction Models for Volume and Biomass of Individual Roots

Descriptions of tree root morphology inform design of belowground biomass and carbon inventories and sampling for research. We studied root morphology of tanoak (Notholithocarpus densiflorus), an important component in mixed evergreen forests of California and Oregon, USA. Tanoak re-sprouts from belowground lignotubers after disturbances, and stores an unknown amount of carbon in coarse roots underground. We sought to ascribe explanatory nomenclature to roots’ morphological features and to identify models describing tanoak root morphology. Twelve tanoak root systems were excavated, dissected, and measured. Roots tapered according to their circumference and location. Larger roots closer to the lignotuber (located at the base of the tree stem) tapered more rapidly per unit of length. Tanoak roots forked frequently. Root cross-sectional area was preserved after forking events (i.e., the sum of cross-sectional areas for smaller roots on one side of the fork correlated with the adjoining large root). Occurrence and quantity of root branches (small roots branching laterally from larger roots) was dependent upon length of the source root segment. Our models of tanoak root morphology are designed to be organized together to estimate biomass of any segment or collection of lateral roots (e.g., roots lost/missed during excavation, or in lieu of destructive sampling), given root diameter at a known distance from the lignotuber. The taper model gives distal- and proximal-end diameters for calculation of volume for segments of root tapering between forks. Frequency of forking and branching can also be predicted. Summing the predicted mass of each lateral root segment, branch, and forked segment would produce an estimate of mass for a contiguous network of lateral roots.

晋北农牧交错带草地生物量对短期放牧强度的响应

放牧是草地的主要利用方式之一,适度放牧可维持草地的生产和生态功能。为探究不同放牧强度如何影响北方农牧交错带草地生物量,本研究依托2016年在山西典型农牧交错带建立的草地放牧试验平台,采用收获法监测了不同放牧强度干扰下植物群落优势种赖草生物量(Leymus secalinus Tzvel.biomass,L.s.B)、地上生物量(Aboveground biomass,AGB)和地下生物量(Belowground biomass,BGB)指标。结果表明:放牧降低了该地区群落地上现存生物量和地下生物量(P<0.01),提高了群落的根冠比(P<0.05);放牧影响优势种赖草生物量在群落地上生物量中的占比,与不放牧相比,轻度放牧和重度放牧对赖草生物量的影响大,而中度放牧的影响小。因此,放牧降低了群落的地上、地下生物量,但中度放牧对优势种赖草生物量的影响小,符合中度干扰假说,为农牧交错带草地科学管理和可持续利用提供理论依据。

模拟降水变化对荒漠草原地上、地下生物量及其分配比例的影响

全球降水格局变化会对草地生态系统植物群落地上、地下生物量产生影响。为探求降水变化对草地群落生物量的影响,本研究在四子王旗荒漠草原设置了4种模拟降水梯度试验,分别为减少自然降水50%、自然降水处理、增加自然降水50%和增加自然降水100%。2018—2020年连续三年测算不同降水梯度处理下植物群落地上、地下生物量及其分配比例,发现2018年到2020年,植物群落地上、地下和总生物量均随降水梯度增加而增加;模拟降水变化对植物群落地上、地下以及总生物量因为样地被围封和降水量不同而产生年际差异。不同降水处理对0~10 cm和20~30 cm中的植物群落地下生物量影响差异显著,20~30 cm土层中,增水处理下的植物群落地下生物量则表现为三年间均为显著递增。减水处理的植物群落生物量向地下分配比例更高(P<0.05)。本试验为维持草地生产力应对未来气候变化提供了理论依据。

大气CO_(2)浓度升高和海平面上升对滨海湿地植物地下生物量的影响

大气CO_(2)浓度升高和海平面上升会通过影响植物的分布和生长状况,继而影响湿地的稳定性。地下生物量是调节潮汐湿地生态系统功能的关键因素,包括土壤有机质的积累和湿地海拔高程的维持。本文通过设置开顶式生长箱(OTC:open top chamber)试验探究不同海拔的3个典型植物群落(SC群落:C_(3)植物为主的群落;MX群落:C_(3)、C_(4)植物混合群落;SP群落:C_(4)植物为主的群落)对CO_(2)浓度升高和海平面上升的响应差异。研究结果显示:CO_(2)浓度升高能够显著增加SC、MX和SP群落的根茎、根和总地下生物量,但年际差异较大。海平面上升显著降低了3个群落植物的根生物量和SC群落高CO_(2)浓度处理下及SP群落对照处理下的总地下生物量,但对根茎却无显著影响。在高盐的条件下,高CO_(2)浓度一定程度上能够缓解高盐分对植物的胁迫,但高CO_(2)浓度的施肥作用下降。对照条件下的SC和MX群落总地下生物量随试验年份延长呈下降趋势,其下降主要是由于海平面的快速上升导致的,而高CO_(2)浓度能减缓其下降趋势,一定程度上抵消胁迫。因此,海平面上升正严重威胁未来湿地的稳定性,而CO_(2)浓度升高能一定程度上缓解海平面上升的危害。

西藏那曲地区高寒草地地下生物量

矮嵩草草甸、藏北嵩草草甸及紫花针茅草原是那曲地区主要的草地类型,通过对其地下生物量的分布特征、地下/地上生物量的关系及其对土壤环境影响的研究发现:(1)这三类植物群落的地下生物量表现为总的T字形趋势下的锯齿状分布,主要分布在0～10cm的草皮层中,而且不同的退化草地,其地下的生物量也不同;(2)各群落的地下生物量和地上生物量密切相关,相关性均呈显著正相关.地下/地上生物量的比值越大,地上生物量就越高.地上生物量的变化不大,而地下生物量变化显著;(3)在高山草甸土中,矮嵩草草甸的地下生物量和土壤的有机质,全N,碱解N的含量及土壤的容重呈相关关系,而与其他的土壤因子相关性不显著.(4)各群落的地下生物量的垂直分布特征及与土壤环境的关系是植物长期适宜高寒生境条件的结果和反映.

不同海拔梯度高寒草地地下生物量与环境因子的关系

以新疆天山南坡的巴音布鲁克高寒草地为对象,研究了不同海拔梯度高寒草地地下生物量的变化及其与环境因子的关系.结果表明:随着海拔的升高,高寒草原、高寒草原化草甸和高寒草甸的地下生物量逐渐增大,二者呈极显著正相关(P<0.01).地下生物量从表层至底层逐渐递减,呈"T"形分布.高寒草原、高寒草原化草甸和高寒草甸0～10cm土层的地下生物量分别占总地下生物量的68.1%、84.1%和86.7%.地下生物量与大气温度呈极显著负相关,与相对湿度和土壤含水量呈极显著正相关(P<0.01),而与有机质、速效氮和pH等无显著相关.

内蒙古温带草地植被的碳储量

草地生态系统在全球碳循环中起着极为重要的作用。大部分草地碳储存在地下,但是实测数据十分匮乏,因此准确估算温带草地植被碳储量对评价草地生态系统碳循环具有重要意义。作为一个区域性资料积累工作,作者对内蒙古温带草地的碳储量进行了大范围的实测研究,以估算该地区草地植被的碳储量。主要结果如下:(1)内蒙古温带草地总面积为58.46×106hm2,总植被碳储量为226.0±13.27Tg C(1 Tg=1012g),平均碳密度为3.44Mg C.hm-2;(2)地下根系储存的碳是地上碳储量的6倍左右,地上、地下生物量碳储量分别为33.22±1.75和193.88±12.6 Tg C,平均碳密度分别是0.51和2.96 MgC.hm-2;(3)不同草地类型的碳储量差异较大,典型草原最大(113.25 Tg C),占草地总碳储量的50%,其次是草甸和草甸草原,荒漠草原碳储量最低(15.37 Tg C)。

放牧对草原生态系统地下生产力及生物量的影响

放牧作为一种人类活动的干扰因子,主要通过动物的采食、践踏及其排泄物的输入对草原生态系统产生影响,这些影响直接作用于草原生态系统的地上部分和土壤,从而影响草原生态系统的物质生产和分配,进而影响到地下生产力和生物量.以蒙古克氏针茅 Stipakrylovii -冷蒿 Artemisiafrigida 草原为研究对象,对自由放牧区和围栏禁牧封育区草原生态系统地下生产力、生物量进行了比较研究.结果表明:自由放牧区草原生态系统地下生产力为147.6g·m-2·y-1,围栏禁牧封育区地下生产力达187.3g·m-2·y-1,二者地下生产力差异显著 α=0.05 ,说明封育保护可以提高过牧草原生态系统的地下生产力.地下生物量在自由放牧区为2032.6g·m-2,其中活地下生物量占54.9%,死地下生物量占45.1%;在围栏禁牧封育区平均为2071.8g·m-2,其中活地下生物量占56.4%,死地下生物量占43.6%,两者没有明显差异.地下生物量在土壤中垂直分布规律在两个试验区均表现为自地表向下呈指数函数减小,主要集中分布在0～30cm的土层.

水分梯度上放牧对内蒙古主要草原群落功能群多样性与生产力关系的影响

应用样线法对放牧对内蒙古草原沿水分梯度分布的主要植物群落:小针茅(Stipaklemenzii)群落、大针茅(Stipagrandis)群落、羊草(Leymuschinensis)群落和羊草杂类草群落多样性、生产力以及两者关系的影响进行了研究,结果表明,除羊草杂类草群落外,物种多样性、生活型多样性和水分生态类型多样性随放牧强度的加大而降低,但适度放牧增加了羊草杂类草群落的上述多样性指标。群落地上现存量一般随放牧强度的增大而下降,但小针茅群落反之,主要与1年生植物猪毛菜(Salsolacollina)的生物量迅速增加有关。除羊草群落外,其他群落0～10cm地下生物量随放牧强度的变化不显著;放牧显著降低羊草群落和羊草杂类草群落0～30cm地下生物量。多样性和生产力间的关系在群落水平上的趋势是不同的,但放牧影响下内蒙古草原4种群落多样性与生产力总体而言呈线性增加关系;同时两者之间的关系还和采用哪种多样性指标和生产力指标有关,用水分生态类型多样性比物种多样性更能反映与地上地下总生产力间的关系,得到放牧影响下内蒙古草原植物群落地上地下总生物量与水分生态类型多样性的回归方程。

封育和放牧对黄土高原典型草原生物量的影响

采用收割法和土柱法研究封育和放牧两种方式对黄土高原典型草原地上、地下生物量的影响。结果表明,1）与放牧区相比,封育显著提高了草原植被的盖度和高度,增加了生物量（地上和地下）。2）封育区与放牧区草地地下生物量的垂直分布均呈典型的倒金字塔型或T字形的锯齿状分布。地下生物量都随土层深度增加而降低、符合指数函数减小规律。3）地下各层生物量变化幅度很大,其中0~10 cm土层与20~30、30~40、40~50 cm土层差异达到极显著（P〈0.01）,与放牧区相比,封育区在0~50 cm各层的地下生物量都高于放牧区。4）地下生物量/地上生物量的值偏大,与当地干旱的气候有关。由于水分条件的不同,封育区地下生物量/地上生物量的值大于放牧区。