Abstract

Soil nutrient distribution is heterogeneous in space and time, potentially altering nutrient acquisition by trees and microorganisms. Ecologists have distinguished “hot spots” (HSs) as areas with enhanced and sustained rates of nutrient fluxes relative to the surrounding soil matrix. We evaluated the spatial and temporal patterns in nutrient flux HSs in two mixed-conifer forest soils by repeatedly sampling the soil solution at the same spatial locations (horizontally and vertically) over multiple seasons and years using ion exchange resins incubated in situ. The climate of these forests is Mediterranean, with intense fall rains occurring following summers with little precipitation, and highly variable winter snowfall. Hot spots formed most often for NO₃⁻ and Na⁺. Although nutrient HSs often occurred in the same spatial location multiple times, HSs persisted more often for PO₄³⁻ NH₄⁺, and NO₃⁻, and were more transient for Ca²⁺, Mg²⁺, and Na⁺. Sampling year (annual precipitation ranged from 558 to 1223 mm) impacted the occurrence of HSs for most nutrients, but season was only significant for PO₄³⁻, NH₄⁺, NO₃⁻, and Na⁺, with HSs forming more often after fall rains than after spring snowmelt. The frequency of HSs significantly decreased with soil depth for all nutrients, forming most commonly immediately below the surficial organic horizon. Although HSs accounted for less than 17% of the sampling volume, they were responsible for 56–88% of PO₄³⁻, NH₄⁺, and NO₃⁻ resin fluxes. Our results suggest that macronutrient HSs have a disproportional contribution to soil biogeochemical structure, with implications for vegetation nutrient acquisition strategies and biogeochemical models.

Graphical abstract

中文翻译：

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中位数不是信息：土壤养分热点对跨年份、季节和深度的生物地球化学结构具有不成比例的影响

摘要

土壤养分分布在空间和时间上是异质的，可能会改变树木和微生物对养分的获取。生态学家将“热点”（HS）区分为相对于周围土壤基质养分通量增强且持续的区域。我们通过使用原位培养的离子交换树脂在多个季节和年份的相同空间位置（水平和垂直）重复采样土壤溶液，评估了两种混合针叶林土壤养分通量 HS 的空间和时间模式。这些森林的气候为地中海气候，夏季过后会出现强烈的秋雨，降水量很少，冬季降雪变化很大。_{NO 3} ^-和Na ⁺最常形成热点。虽然营养物HS经常在同一空间位置多次出现，但PO ₄ ³⁻ NH ₄ ⁺和NO ₃ ^{-的HS更常持续存在，而Ca 2+}、Mg ²⁺和Na ⁺的HS更短暂。采样年份（年降水量范围为 558 至 1223 mm）影响了大多数养分的 HS 发生，但季节仅对 PO ₄ ³⁻、 NH ₄ ⁺、NO ₃ ⁻和 Na ⁺具有显着性，并且在之后更容易形成 HS。秋季的降雨多于春季融雪后的降雨。所有养分的HS频率随着土壤深度的增加而显着降低，最常见的是直接在地表有机层下方形成。尽管HS占采样体积的不到17%，但它们占PO ₄ ³⁻、NH ₄ ⁺和NO ₃ ⁻树脂通量的56-88%。我们的结果表明，常量营养素HS对土壤生物地球化学结构具有不成比例的贡献，对植被养分获取策略和生物地球化学模型具有影响。

图形概要