Seedling establishment and physiological responses to temporal and spatial soil moisture changes
Seedling establishment and physiological responses to temporal and spatial soil moisture changes
复制标题
幼苗建立及对土壤水分时空变化的生理反应
作者：
J. R. Pinto;John D. Marshall;R. K. Dumroese;Anthony S Davis;Douglas R. Cobos
在世界上的许多森林中，夏季（时间因素）会带来干旱条件，导致上层土壤剖面（空间因素）土壤湿度较低，这对幼苗的生长来说是一个潜在的巨大障碍。我们使用黄松幼苗评估了幼苗初始根部深度、外植后干旱期间土壤湿度的时空变化以及随后的幼苗表现之间的关系。变种黄松生长在三个容器中，除了深度外，尺寸相似（即三种库存类型）。土壤湿度模式被量化，生长、气体交换和碳同位素分析被用作种群类型评估的指标。到夏末，土壤湿度在 15 cm 深度处达到最小体积土壤含水量 (θ) 0.078 m3 m−3，在 90 cm 深度处达到 0.15 m3 m−3，这也转化为估计的土壤水势 (Ψsoil) 值分别为 -2.29 和 -0.02 MPa。幼苗的光合作用 (A) 和蒸腾作用 (E) 速率遵循土壤湿度趋势，也在夏末达到季节性低点。初秋时节，降水补充了上部土壤水分，气体交换率几乎翻了一番。在整个生长季节中，种群类型在气体交换率（P≥0.15）、生物量（P≥0.45）、根部穿透深度（P=0.60）或碳同位素特征（P≥0.60）方面没有差异。对于所有幼苗，当年针叶比上年针叶表现出更大的 A 容量（P≤0.01），并且 A 仅与上层土壤剖面的土壤湿度显着相关（15cm；P≤0.03）。在这项研究中，种群类型并不是一个重要因素，这表明它们之间的幼苗对土壤水分的获取没有差异。然而，在土壤水分可用性中观察到的时间和空间变化提供了关于外植时间的关键生物物理信息，因为它与随后的幼苗建立和潜在的根系生长有关。此外，针叶形成、碳增益以及与土壤水深的关系进一步表明了管理土壤水或幼苗种群类型对于幼苗成功存活和生长的重要性。
In many forests of the world, the summer season (temporal element) brings drought conditions causing low soil moisture in the upper soil profile (spatial element)—a potentially large barrier to seedling establishment. We evaluated the relationship between initial seedling root depth, temporal and spatial changes in soil moisture during drought after outplanting, and subsequent seedling performance using seedlings of Pinus ponderosa Laws. var. ponderosa grown in three containers similar in dimension except for depth (i.e. three stocktypes). Soil moisture patterns were quantified and growth, gas exchange, and carbon isotope analysis were used as metrics for stocktype evaluation. Soil moisture reached minimum volumetric soil moisture contents (θ) of 0.078 m3 m−3 at a 15 cm depth and 0.15 m3 m−3 at 90 cm by late summer, which also translated to estimated soil water potential (Ψsoil) values of −2.29 and −0.02 MPa, respectively. Seedling photosynthesis (A) and transpiration (E) rates followed soil moisture trends, also reaching seasonal lows in late summer. In early fall, gas exchange rates nearly doubled following a replenishment of upper-profile soil moisture by precipitation. Over the course of the growing season, stocktypes did not differ in gas exchange rates (P ≥ 0.15), biomass (P ≥ 0.45), root penetration depth (P = 0.60), or carbon isotope signature (P ≥ 0.60). For all seedlings, current-year needles showed greater capacity for A than previous-year needles (P ≤ 0.01), and A was only significantly correlated with soil moisture in the upper soil profile (15 cm; P ≤ 0.03). In this study, stocktype was not a significant factor, suggesting that seedling access to soil moisture was not different among them. The temporal and spatial variation observed in soil moisture availability, however, provides critical biophysical information on outplanting timing as it relates to subsequent seedling establishment and potential root growth. As well, needle formation, carbon gain, and the relationship to soil water depth further indicate the importance for managing soil water or seedling stocktype for successful seedling survival and growth.