Response of Soil Respiration and Its Components to Precipitation Exclusion in Vitex negundo Var. Heterophylla Shrubland of the Middle Taihang Mountain in North China

Assessing the response of soil heterotrophic and autotrophic respiration to climate change is critical for forecasting terrestrial carbon cycle behavior in the future. In the present study, we conducted a drought experiment in Vitexnegundo var. heterophylla shrub ecosystem of the Middle Taihang Mountain. Three precipitation manipulation treatments (natural conditions/ambient precipitation (CK), reduced precipitation by 30% (PE30), and reduced precipitation by 60% (PE60)) were used to study the impact of different levels of precipitation exclusion on total soil respiration (Rs) and its heterotrophic (Rh) and autotrophic (Ra) components. Our results showed that the rates of Rs and its components were significantly decreased under the precipitation exclusion treatments. The proportion of Rh in Rs reduced from 72.6% for CK to 71.9% under PE60. The annual cumulative C fluxes of Rs decreased by 47.8 g C m−2 in PE30 and 106.0 g C m−2 in PE60, respectively. An exponential relationship was observed between the rate of each soil respiration component and soil temperature in all treatments ( p < 0.01). Moreover, each soil respiration component rate was better represented by a quadratic model which included soil moisture ( p < 0.01). However, including both of soil temperature and soil moisture did not explain more variation in soil respiration components compared than the regression model with soil moisture only. In addition, excluding precipitation increased the temperature sensitivity (Q10 values) of Rs and its Ra and Rh components compared to the control. Collectively, our findings suggest that increased drought will inhibit the release of carbon from the soil to the atmosphere, and will likely decrease the contribution of Rh to Rs in this semiarid shrubland ecosystem.

Contrasting Responses of Arbuscular Mycorrhizal Fungal Families to Simulated Climate Warming and Drying in A Semiarid Shrubland

We carried out a 4-year manipulative field experiment in a semiarid shrubland in Southeastern Spain to assess the impacts of experimental warming (W), rainfall reduction (RR) and their combination (W+RR) on the composition and diversity of arbuscular mycorrhizal fungal (AMF) communities in rhizosphere soil using singlemolecule real-time (SMRT) DNA sequencing. Across climate treatments, we encountered 109 AMF OTUs that were assigned to four families: Glomeraceae (93.94%), Gigasporaceae (2.19%), Claroideoglomeraceae (1.95%) and Diversisporaceae (1.92%). The AMF community composition and diversity indices at OTU level were unaffected by the climate manipulation treatments, except for a significant decrease in AMF richness in the W treatment relative to the control. In contrast, AMF family richness decreased significantly in all the climate manipulation treatments relative to the control treatment. Members of the Gigasporaceae and Diversisporaceae families appeared to be highly vulnerable to intensification of heat and drought stress, as their abundances decreased by 67% and 77% respectively, in the W+RR treatment relative to current ambient conditions. In contrast, the relative abundance and dominance of the Glomeraceae family within the AMF community increased significantly under the W+RR treatment, with Glomeraceae being indicator family for the W+RR treatment. The interaction between warming and rainfall reduction had a significant effect on AMF community structure at family level. These findings provide new insights into AM fungal community responses to climate warming and drying in dryland ecosystems.

Evapotranspiration partitioning in a semiarid shrubland and its relation to spring precipitation

<p>ET partitioning is crucial to examine how water and carbon cycles are coupled and to understand the impact of climate change and human activities on ecosystems and water resources. In this study, an optimality-based ecohydrological model is validated and applied for ET partitioning in a Chihuahuan Desert shrubland site in south-eastern Arizona, USA. The ratio of transpiration to evapotranspiration is 49% for the whole period. Evaporation and plant transpiration mainly occur in growing season following the precipitation events. Evaporation responds immediately to rainfall events, while transpiration shows a lagged response of several days to those events. T/ET ratio dynamic in growing season demonstrates different patterns. Some years show low T/ET ratio at the beginning of the growing season. The peak of the T/ET ratio lags behind the rain events. Other years demonstrate stable and relatively high T/ET ratio T/ET ratio is higher than 60% during monsoon when vegetation is active. We find out that spring precipitation especially the size of the precipitation have a significant influence on shrub growth and the T/ET ratio in growing season. These years have dry spring with extremely low spring precipitation, shrubs remain inactive and there is no evident CO<sub>2</sub> uptake during the spring. Under such circumstance, when summer rainfall event happens, shrub has not grown yet, so the most rains are consumed by soil evaporation. In contrast, these years with high T/ET during the growing season all have high amount of spring precipitation. As a consequence, shrubs have developed a certain number of roots and leaves in spring, shrubs recover quickly after the first rain event during the growing season.</p><p>Keywords: evapotranspiration partitioning; evaoration; transpiration; spring precipitation; semiarid shrubland; Chihuahuan Desert.</p>