Effect of precipitation variability on net primary production and soil respiration in a Chihuahuan Desert grassland

Abstract

Precipitation regimes are predicted to become more variable with more extreme rainfall events punctuated by longer intervening dry periods. Water-limited ecosystems are likely to be highly responsive to altered precipitation regimes. The bucket model predicts that increased precipitation variability will reduce soil moisture stress and increase primary productivity and soil respiration in aridland ecosystems. To test this hypothesis, we experimentally altered the size and frequency of precipitation events during the summer monsoon (July through September) in 2007 and 2008 in a northern Chihuahuan Desert grassland in central New Mexico, USA. Treatments included (1) ambient rain, (2) ambient rain plus one 20 mm rain event each month, and (3) ambient rain plus four 5 mm rain events each month. Throughout two monsoon seasons, we measured soil temperature, soil moisture content (y), soil respiration (R s ), along with leaf-level photosynthesis (A net ), predawn leaf water potential (C pd ), and seasonal aboveground net primary productivity (ANPP) of the dominant C 4 grass, Bouteloua eriopoda. Treatment plots receiving a single large rainfall event each month maintained significantly higher seasonal soil y which corresponded with a significant increase in R s and ANPP of B. eriopoda when compared with plots receiving multiple small events. Because the strength of these patterns differed between years, we propose a modification of the bucket model in which both the mean and variance of soil water change as a consequence of interannual variability from 1 year to the next. Our results demonstrate that aridland ecosystems are highly sensitive to increased precipitation variability, and that more extreme precipitation events will likely have a positive impact on some aridland ecosystem processes important for the carbon cycle.

It is getting hotter in here: determining and projecting the impacts of global environmental change on drylands

“…In this direction, reductions in approximately 30 per cent in annual precipitation have been reported to lower daily soil CO 2 efflux by 50 per cent in Mediterranean semiarid shrublands [51]. Moreover, less frequent, more intense rainfall pulses have been found to increase this variable up to 30 per cent in the Chihuahuan Desert [37]. Modelling studies suggest that expected changes in precipitation and temperature, coupled with increases in [CO 2 ], will increase soil respiration in a nonlinear fashion in this desert [84].…”

“…Climate models project an increase in precipitation variability in drylands, including more extreme rainfall events and intense droughts [34]. Large rainfall pulses infiltrate deeper and last longer than smaller rain events [35], and thus even areas undergoing decreases in annual precipitation could experience increased soil moisture if precipitation becomes more variable but is characterized by larger pulses [36,37]. Nevertheless, there is evidence that climate change will exacerbate the aridity of most drylands worldwide, such as the southwestern US [38], the Mediterranean Basin [39], southern Africa [40], Australia [41], South America [42] and China [33].…”

Progress and opportunities for monitoring greenhouse gases fluxes in Mexican ecosystems: the MexFlux network

“…Some examples of relationships that could be tested and validated are those observed between phenology and CO 2 fluxes , control of GPP on RS (Vargas et al, 2011b), or the role of drought and water pulses (Thomey et al, 2011). What follows are examples from measurements at MexFlux sites to illustrate the diversity of patterns and magnitudes of CO 2 fluxes.…”

“…These changes in precipitation patterns can substantially affect carbon sequestration in semiarid rangelands by reducing or increasing water stress within the ecosystem (Thomey et al, 2011, Vargas et al, 2012b.…”

降水格局改变背景下土壤呼吸变化的主要影响因素及其调控过程

“…近年来, 人类活动导致大气中的CO 2 浓度升高, 引起了全球升温和降水格局的改变 (Borken et al, 2002;Chimner et al, 2010;IPCC, 2013)。 多个气候模 型预测结果一致显示, 未来气候变化会带来全球或 局部降水格局的变化 (Fischer et al, 2013;Knapp et al, 2015)。未来降水将在高纬度和部分热带地区增 加, 而在中低纬度和部分亚热带地区减少 (Harper et al, 2005)。 同时, 极端降水事件的发生频率增加, 降 雨强度和降雨时间分布进一步变化 (Thomey et al, 2011;彭琴等, 2012;IPCC, 2013 (Raich & Sehlesinger, 1992;Hanson et al, 2000;Wang et al, …”