Variation in hydraulic redistribution in a desert ecosystem and the role of rhizosphere moisture in stimulating litter decomposition.
Aanderud, Zachary*,1, Richards, James1, 1 University of California, Davis, Davis, CA
ABSTRACT- In deserts where shrub roots span wet and dry soil regions, hydraulic lift or redistribution (HR) increases w in rhizosphere soil in proximity to areas of high C deposition. Since decomposition is often constrained by soil moisture, we hypothesized that increased soil w in densely rooted zones beneath shrubs would result in higher litter decomposition rates. Over two years, we traced soil moisture dynamics and decomposition of leaf and root litter in the presence and absence of roots from Artemisia tridentata and Sarcobatus vermiculatus. Where roots were present, HR occurred for both species but to different magnitudes and durations, with Sarcobatus increasing soil w on a daily basis 0.5-2.0 MPa from June to July and Artemisia increasing soil w 0.5-1.1 MPa from June to August. Despite these large increases in soil moisture from HR, there was net extraction of moisture by roots. By the end of July in both years in root inclusion relative to root exclusion experimental cores, Sarcobatus roots depressed soil w 7.0 MPa, while Artemisia roots depressed soil w 3.0 MPa. Root-induced net soil w depletion by both species slowed decomposition of leaf litter until less than 13% of the total leaf litter remained and decomposition rates approached zero. This pattern was not present for root litter which decomposed much slower under all conditions, suggesting a strong litter quality by soil moisture interaction. Although HR did increase soil w diurnally in the rhizosphere, the overwhelming extraction of soil moisture by roots negated any potential effects of increased rhizosphere moisture on decomposition. Thus, contrary to our hypothesis increased rhizosphere moisture by HR did not stimulate litter decomposition.
Key words: rhizosphere, hydraulic redistribution, desert
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