DataSheet_1_Precipitation modulates the net effect of solar radiation on litter decomposition and CO2 emission - a meta-analysis.docx

IntroductionSolar radiation plays a crucial role in the decomposition of litter and the cycling of nutrients. Previous studies have investigated that the net effect of solar radiation on litter decomposition depends on the balance of its facilitative and inhibitory effects on microbial activity; however, a gap in understanding the mechanism by which precipitation affects the net effect of solar radiation and the mechanism of litter decomposition on a global scale was observed.
MethodsIn addressing this gap, a comprehensive meta-analysis of 351 data points from 37 published studies was conducted to estimate the sole radiation effect and interactive effect of solar radiation and precipitation on a global scale, as well as how they vary at different precipitation levels. In addition, the importance of influential factors regulating the net effect of solar radiation on litter decomposition was assessed to identify the key drivers of the response of mass loss to solar radiation at different precipitation levels.
ResultsOur findings indicated that solar radiation largely regulates litter decomposition, and the direction and magnitude are potentially dependent on the precipitation regime. In addition, solar radiation significantly increased mass loss and decreased the nutrient remaining. Furthermore, the effects of solar radiation on mass loss, C remaining, and N remaining were found to be similar among areas with precipitation levels below 200 and above 800 mm and greater than in areas with precipitation levels between 200-400 mm and 400-800 mm. The effect of solar radiation on CO2 emissions varied from 13.97% when precipitation was below 200 mm to −0.707% when precipitation was between 200 and 400 mm.
ConclusionClimatic factors determine the response ratio of mass loss to solar radiation in arid lands, whereas the initial litter characteristics have a great influence on the response of mass loss to solar radiation in ecosystems that are not moisture limited. The effect of precipitation on the photodegradation mechanism of litter was primarily achieved by influencing the decomposition of lignin, and the main effect of solar radiation on litter decomposition will shift from the positive effect of “photopriming” to the negative effect of “microbial inhibition” with the increase of precipitation. Our findings can provide a comprehensive understanding of litter decomposition patterns on a global scale, and our results showed that CO2 emissions from photodegradation will be lessened by precipitation, which is important in predicting CO2 emission and separating sources of CO2 under future increasing precipitation scenarios, particularly in arid lands.

引言：太阳辐射在枯落物分解（litter decomposition）与养分循环过程中发挥着至关重要的作用。既往研究表明，太阳辐射对枯落物分解的净效应取决于其对微生物活性的促进与抑制作用之间的平衡；然而，目前仍存在全球尺度下降水如何影响太阳辐射净效应、以及枯落物分解机制的认知空白。

研究方法：为填补这一研究空白，本研究整合37项已发表研究中的351组数据点开展全面荟萃分析（meta-analysis），以估算全球尺度下单辐射效应、太阳辐射与降水的交互效应，同时分析二者在不同降水梯度下的变化规律。此外，本研究还评估了调控太阳辐射对枯落物分解净效应的关键影响因子的重要性，以明确不同降水梯度下枯落物质量损失（mass loss）对太阳辐射响应的核心驱动因素。

研究结果：研究结果表明，太阳辐射可显著调控枯落物分解过程，其作用方向与强度大概率取决于降水格局。此外，太阳辐射可显著提升枯落物质量损失，并降低养分残留量。进一步分析显示，太阳辐射对质量损失、碳残留量与氮残留量的影响在年降水量低于200mm和高于800mm的区域中表现相似，且其效应强度显著高于降水介于200~400mm与400~800mm的区域。太阳辐射对二氧化碳（CO₂）排放的影响随降水梯度变化：在年降水量低于200mm的区域中效应为13.97%，而在200~400mm的区域中则为-0.707%。

结论：在干旱地区，气候因子决定了枯落物质量损失对太阳辐射的响应系数；而在水分不受限的生态系统中，枯落物初始特性则对该响应过程发挥主导调控作用。降水对枯落物光降解（photodegradation）机制的调控作用主要通过影响木质素（lignin）分解实现；随着降水增加，太阳辐射对枯落物分解的主导效应将从“光引发（photopriming）”的正向作用转变为“微生物抑制（microbial inhibition）”的负向作用。本研究结果可增进全球尺度下枯落物分解格局的综合认知；同时发现降水可削弱光降解过程产生的二氧化碳排放，这对于未来降水增加情景下的二氧化碳排放预测与源解析具有重要意义，在干旱地区尤为如此。