A test of the seasonal availability of water hypothesis in a C3/C4 mixed grassland

Understanding how cool-season C3 and warm-season C4 grasses will respond to climate change is critical for predicting future grassland functioning. With warming, C4 grasses are expected to increase relative to C3 grasses. But, alterations in the seasonal availability of water may also influence C3/C4 dynamics because of their distinct seasons of growth. To better understand how shifts in the seasonal availability of water can affect ecosystem function in a northern mixed grass prairie in southeastern Wyoming, we reduced early season rainfall (April – June 2021) using rainout shelters and added the amount of excluded precipitation during the latter half of the growing season (July-September), effectively shifting spring rainfall to summer rainfall.  As expected, this shift in precipitation seasonality influenced patterns of soil water availability, leading to increased soil respiration in the summer months and sustained canopy greenness throughout the growing season. Despite these respon..., Experimental Design
Before the 2021 growing season, we established twenty 1 m2 plots (n=10 per treatment). Plots were separated by at least 3 m, and aluminum flashing was installed (10 cm belowground and 5 cm aboveground) 20 cm outside of the plot perimeter to reduce surface and shallow soil water movement into and out of each plot.  Rainout shelter roofs (2.44 m × 3.05 m made of clear corrugated polycarbonate, Suntuf, Palram Americas) that were larger than the 1 m2 plots were then placed over ten of the plots. Roofs were initially installed 80 cm above the ground at a slight angle to allow water to drain away from the plot; later in the season, the shelters were raised to 100 cm. Although previous work has demonstrated that these shelters have minimal influence on the microclimate (Loik et al. 2019; Post and Knapp 2020; Hoover et al. 2022), we monitored soil temperatures at 10 cm weekly and evaluated light transmission under the roofs using a 1-m linear quantum light sensor (Decagon Ac..., , # Data from: A test of the seasonal availability of water hypothesis in a C3/C4 mixed grassland

Abstract:
To better understand how shifts in the seasonal availability of water can affect ecosystem function in a
northern mixed grass prairie in southeastern Wyoming, we reduced early season rainfall (April June 2021) using rainout shelters and added the amount of excluded precipitation during the latter half of the growing season (July-September), effectively shifting spring rainfall to summer rainfall. As expected, this shift in precipitation seasonality influenced patterns of soil water availability, leading to increased soil respiration in the summer months and sustained canopy greenness throughout the growing season. Despite these responses, there were no significant differences in C3 aboveground net primary production (ANPP) between the seasonally shifted treatment (SEAS) and the plots that received ambient (AMB) precipitation. This was likely due to the high levels of spring soil m...

阐明冷季型C3草本植物（cool-season C3 grasses）与暖季型C4草本植物（warm-season C4 grasses）对气候变化的响应规律，对预测未来草原生态系统功能至关重要。在气候变暖背景下，C4草本植物的相对占比预计将高于C3草本植物。此外，由于两类草本的生长季存在显著差异，水分季节可利用性的改变同样会影响C3/C4草本的群落动态。
为深入探究水分季节可利用性变化如何影响怀俄明州东南部北部混合草原的生态系统功能，本研究于2021年利用避雨棚（rainout shelters）减少早春时段（2021年4月至6月）的降雨量，并将截留的降水在生长季后半段（7月至9月）施加至样地，从而将春季降雨人为转移至夏季。
正如预期，降水季节格局的改变显著影响了土壤水分可利用性模式，导致夏季土壤呼吸速率升高，且在整个生长季维持了稳定的冠层绿度（canopy greenness）。尽管出现了上述响应……
## 实验设计
在2021年生长季开始前，我们共设置20个1 m²的样地（每个处理10个重复），样地之间间隔至少3 m。在每个样地周边20 cm处安装铝制挡箔（地下埋深10 cm，地上露出5 cm），以减少地表及浅层土壤水在样地间的进出。随后，为其中10个样地搭建尺寸大于1 m²的避雨棚屋顶（2.44 m × 3.05 m，采用Palram Americas公司生产的Suntuf品牌透明波纹聚碳酸酯板材制作）。屋顶初始安装高度为距地面80 cm，呈轻微倾斜角度以确保雨水远离样地排出；生长季中后期将棚架升高至100 cm。尽管已有研究表明此类避雨棚对微气候的影响极小（Loik等，2019；Post & Knapp，2020；Hoover等，2022），我们仍每周监测10 cm深度处的土壤温度，并使用1米线性量子光传感器（Decagon Ac……）对棚下的光透射率进行评估。
# 数据来自：《C3/C4混合草原水分季节可利用性假说的检验》
摘要：
为深入探究水分季节可利用性变化如何影响怀俄明州东南部北部混合草原的生态系统功能，我们于2021年利用避雨棚减少早春时段（2021年4月至6月）的降雨量，并将截留的降水在生长季后半段（7月至9月）施加至样地，从而将春季降雨人为转移至夏季。正如预期，降水季节格局的改变显著影响了土壤水分可利用性模式，导致夏季土壤呼吸速率升高，且在整个生长季维持了稳定的冠层绿度。尽管出现了上述响应，季节移位处理组（SEAS）与自然降水对照组（AMB）的C3草本地上净初级生产力（aboveground net primary production, ANPP）并无显著差异。这一结果可能源于春季较高的土壤含水量……