Liquefaction and FTIR analysis of two desert shrubs Salix psammophila and Caragana intermedia

In order to extend the investigation of the characteristics of desert shrub liquefaction and the structure of liquefied desert shrubs, we studied the liquefaction of Salixpsammophila and Caragana intermedia in the presence of phenol and used FTIR analysis on unliquefied and liquefied S. psammophila and C. intermedia. The results showed that the liquefaction effects are enhanced with an increase in temperature, catalyst content and liquid ratio. FTIR analysis proved that more active functional groups appeared after S. psammophila and C. intermedia were liquefied in the presence of phenol. These results can provide a theoretical basis for the further utilization of liquefied S. psammophila and C. intermedia and the development of desert shrubs in a new utilization field.

Rainfall partitioning by desert shrubs in arid regions

We measured the rainfall partitioning among throughfall, stemflow, and interception by desert shrubs in an arid region of China, and analyzed the influence of rainfall and canopy characteristics on this partitioning and its ecohydrological effects. The percent-ages of total rainfall accounted for by throughfall, stemflow, and interception ranged from 78.85±2.78 percent to 86.29±5.07 per-cent, from 5.50±3.73 percent to 8.47±4.19 percent, and from 7.54±2.36 percent to 15.95±4.70 percent, respectively, for the four shrubs in our study (Haloxylon ammodendron, Elaeagnus angustifolia, Tamarix ramosissima, and Nitraria sphaerocarpa). Rain-fall was significantly linearly correlated with throughfall, stemflow, and interception (P < 0.0001). The throughfall, stemflow, and interception percentages were logarithmically related to total rainfall (P < 0.01), but were quadratically related to the maximum 1-hour rainfall intensity (P < 0.01). The throughfall and stemflow percentages increased significantly with increasing values of the rainfall characteristics, whereas the interception percentage generally decreased (except for average wind speed, air temperature, and canopy evaporation). Regression analysis suggested that the stemflow percentage increased significantly with increasing crown length, number of branches, and branch angle (R2 = 0.92, P < 0.001). The interception percentage increased significantly with increasing LAI (leaf area index) and crown length, but decreased with increasing branch angle (R2 = 0.96, P < 0.001). The mean funnelling percentages for the four shrubs ranged from 30.27±4.86 percent to 164.37±6.41 percent of the bulk precipitation. Much of the precipitation was funnelled toward the basal area of the stem, confirming that shrub stemflow conserved in deep soil layers may be an available moisture source to support plant survival and growth under arid conditions.

Drought Resistance of Twelve Desert Shrubs at Seedling Stage of Ulan Buh Desert Ecosystem

[Objective] To establish drought resistance evaluation index system of desert shrubs,and provide scientific support for selecting quality tree species.[Method] Taking 2-year-old seedlings of 12 desert shrubs in Ulan Buh Desert ecosystem as the test materials,7 water physiological indexes were tested,principal component analysis and cluster analysis were applied to explore drought resistance of the shrubs.[Results](a) Water potential of Ephedra distachya Linn.,Nitraia tangutorum Bobr.,Caragana korshinski Kom.was lower than that of the other 9 species;bound water content(V_a) and bound water/free water ratio(V_a/V_s) of Zygophyl um xanthoxylon Maxim.was 64.20% and 3.3,higher than the others';transpiration rate of Atraphaxis bracteata A.Los.,Nitraia tangutorum Bobr.and Tamarix elongata Ldb.was significantly lower than the others';constant weight time of Haloxylon ammodendron(C.A.Mey.) Bunge and Ephedra distachya Linn.was the longest(144 h);residual moisture content of Ammopiptanthus mongolicus Maxim.was the highest(44.80%).(b) Water potential,bound water/free water(V_a/V_s),residual moisture content,bound water,constant weight time,and transpiration rate had great impact on drought resistance of plant,and the accumulative variance contribution rate achieved 87.59%.[Conclusion] According to the drought resistance,the 12 species were classified into 3 categories,namely shrubs with strong drought resistance(Ephedra distachya Linn.),shrubs with moderate drought resistance(Haloxylon ammodendron(C.A.Mey.) Bunge,Nitraia tangutorum Bobr.,and Zygophyllum xanthoxylon Maxim.);shrubs with poor drought resistance(Hedysarunn scoparium Fisch,Hedysarum mongolicum Turcz.,Tamarix elongata Ldb.,Caragana korshinskii Kom.,Ammopiptanthus mongolicus Maxim.,Atraphaxis bracteata A.Los.,Cal igonum mongolicum Mattei.,and Caragana microphylla Lam.).

Effects of shrubs and precipitation on spatial-temporal variability of soil temperature in microhabitats induced by desert shrubs

Soil temperatures at 0, 5, 10 and 20 cm depths were monitored cominuously at different microhabitats （beneath shrub canopy （BSC）; bare intershrub spaces （BIS）） induced by xerophytic shrub （Caragana korshinskii Kom.） canopy, respectively. We mainly aimed to assess the effects of shrub canopy and precipitation on the spatial-temporal variability of soil temperature. Results indi- cate that both precipitation and vegetation canopy significantly affect soil temperature. In clear days, soil temperatures within the BSC area were significantly lower than in the BIS at the same soil depth due to shading effects of shrub canopy. Diurnal variations of soil temperature show a unimoclal sinusoidal curve. The amplitude of soil temperature tended to decrease and a hysteresis of di- urnal maximum soil temperature existed at deeper soil layers. Vertical fluctuations of soil temperature displayed four typical curves. In the nighttime （approximately from sunset to sunrise）, surface temperature within the BSC area was higher than in the BIS. In rainy days, however, soil temperatures were affected mainly by precipitation and the shrub canopy had a negligible effect on soil temperature, and little difference in soil temperature at the same soil depth was found between the BSC area and in the BIS. Diurnal variations in soil temperature decreased exclusively as rainfall continued and the vertical fluctuations of soil tempera~＇e show an increased tendency with increasing soil depth.

Advanced studies on adaptation of desert shrubs to environmental stress

The combined stress of drought, high temperature and excessive light characterizes the desert area. In order to survive the desert habitat, desert shrubs have evolved a number of special eco-physiological mechanisms to resist environmental stress during long-term evolution. In this paper, adaptation mechanisms of desert shrubs to environmental stress are reviewed in terms of morphological structure, water potential, photosynthesis and water use efficiency, transpiration and stomatal conductance, osmotic adjustment and anti-oxidation protection. In addition, some suggestions for future research are proposed.

Resorptions of 10 mineral elements in leaves of desert shrubs and their contrasting responses to aridity

Aims We aim to investigate variations in the resorption efficiencies of 10 mineral nutrients[i.e.nitrogen(N),phosphorus(P),potassium(K),magnesium(Mg),calcium(Ca),manganese(Mn),zinc(Zn),alu-minum(Al),iron(Fe)and copper(Cu)]in leaves of desert shrubs and to explore effects of aridity on resorption efficiency of these nutrients.Methods Plant samples were collected from 10 sites in northern Xinjiang Uygur Autonomous Region of China.Samples of green and senesced leaves were analysed to determine concentrations of N,P,K,Mg,Ca,Mn,Zn,Al,Fe and Cu and thus the nutrient resorption efficiency.Important Findings The mean nutrient concentrations in the desert shrubs varied,with the stoichiometric ratio Ca:N(19.3 mg g−1):K(10.5 mg g−1):Mg:P(1.01 mg g−1):Al:Fe:Mn:Zn:Cu(4.78 mg kg−1)=4038:2950:2199:1816:211:37:32:11:2:1 in green leaves;and Ca:N(12.6 mg g−1):Mg:K(7.6 mg g−1):P(0.56 mg g−1):Fe:Al:Mn:Zn:Cu(2.85 mg kg−1)=5583:3710:2943:2523:178:133:119:19:3.7:1 in senesced leaves.Resorption generally occurred for six elements(N,P,K,Cu,Mg and Mn,with average resorption efficiency 47.8%,52.0%,38.6%,41.0%,12.7%and 7.89%,respectively)during leaf senescence,while the other four nutrients tended to accumulate in senesced leaves,showing averagely negative resorption efficiencies[Ca(-3.87%),Al(−57.1%),Zn(−62.6%),Fe(−89.6%)].Aridity showed strikingly different effects on the resorption process of the 10 nutri-ents.Of the four elements with totally(N/P/K)or mostly(Cu)posi-tive observations of resorption efficiency,their resorption generally decreased with aridity,suggesting that drought stress had negative effects on the resorption efficiencies of these elements.In contrast,with at least one-third observations of resorption efficiency being negative,the other elements(Mg/Mn/Ca/Zn/Al/Fe)showed gener-ally increasing resorptive tendency with aridity,except for Zn.This research provided a systematic analysis on the large variation and contrasting responses of the resorption of multi-elements to aridity in typical desert shrubs.Our findings foster the understanding of nutrient resorption patterns of desert plants and enable us to better predict the contrastive effects of drought stress on the cycling of diverse nutrients and the consequent stoichiometric decoupling in plants of desert ecosystems.

Root distribution of three dominant desert shrubs and their water uptake dynamics

Aims Root architecture is a crucial determinant in the water use of desert shrubs.However,lack of integrated research on the root functional type and water uptake dynamic hinders our current understanding of the water-use strategies of desert species.Methods A field experiment was conducted to investigate the root functional type of three dominant desert species,Haloxylon ammodendron,Nitraria tangutorum and Calligonum mongolicum,and the dynam-ics of their root water uptake.the stem sap flow and microclimate were monitored,and the intact root systems of these shrubs were excavated in their native habitats on the oasis-desert ecotone of northwestern china during the summer of 2014.Important Findings Based on root functional type,H.ammodendron is phreatophytic,while N.tangutorum and C.mongolicum are non-phreatophytic species,which means H.ammodendron can utilize multiple potential water sources,N.tangutorum and C.mongolicum mainly utilize shallow and middle soil water.the average root water uptake rates(RWU)of H.ammodendron,N.tangutorum and C.mongolicum were 0.56(±0.12),1.18(±0.19)and 1.31(±0.30)kg m^(−2)h^(−1),respectively,during the experimental period;the contributions of night-time RWU to total water uptake amount for the corresponding species were 12.7,2.9 and 10.6%,respec-tively.the diurnal and seasonal dynamics of RWU in the three species were significantly different(P<0.05),and closely related to environmental variables,especially to photosynthetically active radiation and vapor pressure deficit.Our results suggested that the three species have distinct water-use patterns in combination with the patterns of root distribution,which may alleviate water competition during long-term water shortages.H.ammodendron appears to be more drought tolerant than the other species due to its use of multiple water sources and stable water uptake rates during growing season.

Precipitation Pulses and Soil CO_2 Emission in Desert Shrubland of Artemisia ordosica on the Ordos Plateau of Inner Mongolia,China

Precipitation is the major driver of ecosystem functions and processes in semiarid and arid regions. In such waterlimited ecosystems, pulsed water inputs directly control the belowground processes through a series of soil drying and rewetting cycles. To investigate the effects of sporadic addition of water on soil CO2 effux, an artificial precipitation event （3 mm） was applied to a desert shrub ecosystem in the Mu Us Sand Land of the Ordos Plateau in China. Soil respiration rate increased 2.8 4.1 times immediately after adding water in the field, and then it returned to background level within 48 h. During the experiment, soil CO2 production was between 2 047.0 and 7 383.0 mg m^-2. In the shrubland, soil respiration responses showed spatial variations, having stronger pulse effects beneath the shrubs than in the interplant spaces. The spatial variation of the soil respiration responses was closely related with the heterogeneity of soil substrate availability. Apart from precipitation, soil organic carbon and total nitrogen pool were also identified as determinants of soil CO2 loss in desert ecosystems.

Effects of sand burial on survival and growth of Artemisia halodendron and its physiological response

There is a great deal of literature on the effects of sand burial upon the survival and growth of desert plants, but the physiological adaption mechanisms of desert plants to sand burial have as yet rarely been studied. Artemisia halodendron is widely distributed in the semi-arid deserts of China and is a dominant species in semi-moving dune vegetation. The growth and physiological properties ofA. halodendron seedlings under different sand burial depths were studied in 2010 and 2011 in the Horqin Sand Land, Inner Mongolia, to better understand the ability and physiological mechanism by which desert plants withstand sand burial. The results showed that A. halodendron as a prammophyte species had a stronger ability to withstand sand burial compared to non-prammophytes, with some plants still surviving even if buried to a depth reaching 225% of seedling height. Although seedling growth was inhibited significantly once the depth of sand burial reached 50% of the seedling height, seedling survival did not decrease significantly until the burial depth exceeded 100% of the seedling height. Sand burial did not result in significant water stress or MDA （Malondialdehyde） accumulation in the seedlings, but membrane permeability increased significantly when the burial depth exceeded 100% of the seedling height. After being subjected to sand burial stress, POD （Peroxidase） activity and proline content increased significantly, but SOD （Superoxide Dismutase） and POD activities and soluble sugar content did not. The primary mechanism resulting in in- creased mortality and growth inhibition were that cell membranes were damaged and photosynthetic area decreased when subjected to the severe stress of sand burial, while proline and POD played key roles in osmotic adjustment and protecting cell membranes from damage, respectively.

Seasonal effect of three desert halophytes on soil microbial functional diversity

The objective of this study was to evaluate the effect of some plant ecophysiological adaptations on soil microbial functional diversity in a Negev Desert ecosystem.Soil samples from the upper 0–10 cm layer were collected at the study site under three species of halophyte shrubs,Zygophyllum dumosum,Hammada scoparia,and Reaumuria negevensis.These halophytes represent the most typical cover of the Negev Desert and each of them develops complex strategies that enable greater adaptation and hence,survival.The microhabitat of the shrubs showed differences in trends and magnitude of organic matter content,electrical conductivity,total soluble nitrogen,microbial functional diversity,and C compound utilization.The trends are assumed to be driven by various mechanisms of shrub adaptation in order to be able to survive the harsh desert environment.This study provides evidence that ecophysiological strategies developed by halophytes force microbial communities(from the point of view of activity,composition,and substrate utilization)to adapt to a beneficial plant-microorganism relationship.

Ecological Wood Adaptation and Horizontal Variations of Vessel Element and Fibre Length of Calligonum mongolicum

Wood anatomy of Calligonum mongolicum Turcz. was described from an ecological perspective. This species showed similar wood structure to that species published in the same genus. This species has distinct growth ring boundaries, ring-porosity, distinct helical thickenings, simple perforation plate, nonseptate fibre, axial parenchyma, uni- or 2-5-seriate heterogeneous rays, and alternate intervessel pitting. It was observed that there is a slightly increase of fibre length as the diameter from the pith increases. However, the vessel element length remains more or less constant from pith to bark. Furthermore, the relationships between anatomical features and adaptability to desert environments were discussed.