Modelling the effect of changing precipitation inputs on deep soil water utilization

Abstract

Forests in the Southeastern United States are predicted to experience future changes in seasonal patterns of precipitation inputs as well as more variable precipitation events. These climate change‐induced alterations could increase drought and lower soil water availability. Drought could alter rooting patterns and increase the importance of deep roots that access subsurface water resources. To address plant response to drought in both deep rooting and soil water utilization as well as soil drainage, we utilize a throughfall reduction experiment in a loblolly pine plantation of the Southeastern United States to calibrate and validate a hydrological model. The model was accurately calibrated against field measured soil moisture data under ambient rainfall and validated using 30% throughfall reduction data. Using this model, we then tested these scenarios: (a) evenly reduced precipitation; (b) less precipitation in summer, more in winter; (c) same total amount of precipitation with less frequent but heavier storms; and (d) shallower rooting depth under the above 3 scenarios. When less precipitation was received, drainage decreased proportionally much faster than evapotranspiration implying plants will acquire water first to the detriment of drainage. When precipitation was reduced by more than 30%, plants relied on stored soil water to satisfy evapotranspiration suggesting 30% may be a threshold that if sustained over the long term would deplete plant available soil water. Under the third scenario, evapotranspiration and drainage decreased, whereas surface run‐off increased. Changes in root biomass measured before and 4 years after the throughfall reduction experiment were not detected among treatments. Model simulations, however, indicated gains in evapotranspiration with deeper roots under evenly reduced precipitation and seasonal precipitation redistribution scenarios but not when precipitation frequency was adjusted. Deep soil and deep rooting can provide an important buffer capacity when precipitation alone cannot satisfy the evapotranspirational demand of forests. How this buffering capacity will persist in the face of changing precipitation inputs, however, will depend less on seasonal redistribution than on the magnitude of reductions and changes in rainfall frequency.

Within-Site Variation in Seedling Survival in Norway Spruce Plantations

“…Increases in variation in annual climatic parameters, due to future climate change, may increase the value of robust predictions of drought-related mortality in scarification method decisions. Examples of such ecophysiological responses to interactive climate, site and management variations might not be common yet in northern Europe, but there are numerous examples from other regions with plantation forestry [20,21]. There were almost equal distributions of containerized and bare-rooted seedlings, and no difference in their survival rate was detected in this study, in accordance with findings of several experimental studies that both seedling types have pros and cons [22,23].…”

Throughfall Reduction × Fertilization: Deep Soil Water Usage in a Clay Rich Ultisol Under Loblolly Pine in the Southeast USA

“…In deep soil horizons, lower soil moisture could be caused by higher root water uptake or continued soil drainage. The absence of VWC values above θ s (Figure 4), however, suggests limited potential for drainage and therefore, lower VWC in 2-3 m soils are likely caused by higher root water uptake (the presence of roots in deep soil was reported in Qi et al, 2018a).…”

“…Studies at this location and other companion sites using the same trough structure to reduce throughfall have already demonstrated impacts on soil moisture and plant water usage responses such as transpiration (Samuelson et al, 2014Ward et al, 2015;Maggard et al, 2016Maggard et al, , 2017Wightman et al, 2016). Finally, using the same experiment site, a study modeling the effect of changing precipitation inputs on deep soil water utilization was able to calibrate and validate water balances using the same field measurements (Qi et al, 2018a).…”

“…At the 19-year-old site, <20% of water was stored in the top 30 cm of soil and soil at 60-140 cm depth contributed a larger amount of water to transpiration relative to 10-60 cm soils during dry periods (Domec et al, 2012). A modeling study manipulating precipitation inputs to a pine stand showed that when annual precipitation input was reduced more than 30%, plants required stored soil water to satisfy transpirational demands and the contribution of deep soil water to transpiration increased as precipitation declined (Qi et al, 2018a). Considering the uncertainty in climate change, deep soil water could play a more vital role to buffer the effects of drought as stands age.…”

Characteristics and underlying mechanisms of plant deep soil water uptake and utilization: Implication for the cultivation of plantation trees

“…。 此外, 了解树木对深层土壤水 的吸收利用特征还可帮助深入认识树木对干旱和气 候 变 化 的 响应 与 适 应 机制 (Nepstad et al, 1994;Broedel et al, 2017;Christina et al, 2017)、树木与环 境 的 互 作 机 制 (Nepstad et al, 1994; 刘 晓 丽 等 , 2014)、树木的生长与生存策略 (Xu & Li, 2008;Pinheiro et al, 2016;Zunzunegui et al, 2017)、物种 间的共存与竞争机制( Barron-Gafford et al, 2017;Chitra-Tarak et al, 2018;de Deurwaerder et al, 2018;Guderle et al, 2018), 并进而为林地水分管理策略 的制定 (Adriano et al, 2017;Christina et al, 2017)、 植被恢复 (陈亚宁等, 2016;Sun et al, 2018)、生物多 样性保护 (Lindh et al, 2014)、林分结构配置与优化 (Germon et al, 2017; 苗博等, 2017)、林木遗传育种 (Pinheiro et al, 2016)、现有森林抚育措施优化(如间 伐木的选择等) (Hardanto et al, 2017)、 林地水文模型 的优化和构建 (Pinheiro et al, 2016;Fan et al, 2017) 等提供依据。因此, 随着同位素、根系液流监测、 土壤水分测定等技术的发展, 树木对深层土壤水分 吸收利用的研究在近年来逐渐被广泛关注, 有必 要对相关研究进行系统归纳与总结。 深层根系是植物借以吸收深层土壤水的唯一工 具, 其在树木水分关系中的重要性早在近一个世纪 以前就被人们所关注 (Hayes & Stoeckler, 1935), 其 对深层土壤养分吸收、土壤物理化学风化、碳地球 化学循环、土壤动物和微生物群落等的影响也逐渐 被了解 (McCulley et al, 2004;Maeght et al, 2013;Billings et al, 2018) (Maeght et al, 2013;Pierret et al, 2016) Yang et al, 2017;Zunzunegui et al, 2017;Qi et al, 2018) (Jackson et al 1997;王政权和郭大立, 2008;Ma et al, 2018), 其在深土层中的结构决定了 树木对深层土壤资源的"觅取"范围和效率, 并进而 对区域甚至全球水、碳、养分循环和气候产生重要 影 响 (Nepstad et al, 1994;Jackson et al, 1997;Schenk & Jackson, 2002b;Lee et al, 2005;…”