Soil carbon and nitrogen dynamics throughout the summer drought in a California annual grassland

Schaeffer, Sean M.; Homyak, Peter M.; Boot, Claudia M.; Roux-Michollet, Dad; Schimel, Joshua P.

doi:10.1016/j.soilbio.2017.08.009

Cited by 88 publications

(74 citation statements)

References 77 publications

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“…4a, b). A decrease in microbial activity due to an increase in soil moisture has been reported in the Mediterranean region (Parker and Schimel 2011, Sullivan et al 2012, Schaeffer et al 2017, which has similar climatic conditions as the present study. Although no significant relation between moisture content and nitrification rates (other NH þ 4 consumption process; Fig.…”

Section: Discussionsupporting

confidence: 89%

Gross nitrogen transformation rates in semiarid tropical soils under different salinity and vegetation conditions

Sharma

Kumar

2020

Ecosphere

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Exacerbated inundations and saltwater intrusions due to sea‐level rise can significantly alter the ecology of low‐lying coastal drylands by affecting their nutrient cycling and productivity. During the present study, controls on production and consumption of nitrogen in soils of semiarid tropical climate with different levels of vegetation–salinity–moisture condition were investigated using 15N isotope dilution experiments. For this purpose, soils were collected from five land types including two in salt flat and one each in grassland (GL), wetland (WL), and an agricultural field. Soils with no vegetation, high salinity, and high moisture (salt flats) showed significant decline in gross production of nitrogen (mineralization rate: 0.21 ± 0.10 mg N·kg−1·d−1; nitrification rate: 0.27 ± 0.17 mg N·kg−1·d−1) compared to soils with vegetation, low salinity, and low moisture (GL, WL, and agricultural) (mineralization rate: 2.47 ± 1.74 mg N·kg−1·d−1; nitrification rate: 1.43 ± 1.30 mg N·kg−1·d−1). Backward stepwise regression analysis of the results indicated salinity to be the most important factor controlling nitrogen transformation rates. It is likely that soils undergoing frequent seawater exposure or excessive evaporation may experience slowdown in nitrogen cycling due to salinization leading to reduced nutrient production and consumption. Due to climate change, the areal extent of coastal drylands undergoing such decline in nutrient production is likely to increase, eventually leading to loss of productivity and desertification.

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Section: Discussionsupporting

confidence: 89%

Gross nitrogen transformation rates in semiarid tropical soils under different salinity and vegetation conditions

Sharma

Kumar

2020

Ecosphere

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“…, Schaeffer et al. ). If microbial death occurs by osmotic stress during rewetting, then WEOC should have been highest in plots with the highest microbial biomass, but it was not—microbial biomass was highest in plots with plants where WEOC was lowest.…”

Section: Discussionmentioning

confidence: 99%

“…, Schaeffer et al. ). That slaking of micropores releases previously inaccessible WEOC is also consistent with the rejuvenation of CO 2 pulses from one dry season to the next despite excluding plant C inputs (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…, Schaeffer et al. ). Disentangling how moisture regulates microbial access to C, and the fate of C is a necessary step toward validating assumptions built into models that predict C sequestration in soil organic matter (SOM) (Todd‐Brown et al.…”

Section: Introductionmentioning

confidence: 99%

“…, Schaeffer et al. ). In this way, drying can increasingly concentrate substrates as soils become hydrologically decoupled, generating pools of bioavailable materials that can diffuse to microbes when soils wet up (Manzoni and Katul , Homyak et al.…”

Section: Introductionmentioning

confidence: 99%

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Effects of altered dry season length and plant inputs on soluble soil carbon

Homyak

Blankinship

Slessarev

et al. 2018

Ecology

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Soil moisture controls microbial activity and soil carbon cycling. Because microbial activity decreases as soils dry, decomposition of soil organic matter (SOM) is thought to decrease with increasing drought length. Yet, microbial biomass and a pool of water-extractable organic carbon (WEOC) can increase as soils dry, perhaps implying microbes may continue to break down SOM even if drought stressed. Here, we test the hypothesis that WEOC increases as soils dry because exoenzymes continue to break down litter, while their products accumulate because they cannot diffuse to microbes. To test this hypothesis, we manipulated field plots by cutting off litter inputs and by irrigating and excluding precipitation inputs to extend or shorten the length of the dry season. We expected that the longer the soils would remain dry, the more WEOC would accumulate in the presence of litter, whereas shortening the length of the dry season, or cutting off litter inputs, would reduce WEOC accumulation. Lastly, we incubated grass roots in the laboratory and measured the concentration of reducing sugars and potential hydrolytic enzyme activities, strictly to understand the mechanisms whereby exoenzymes break down litter over the dry season. As expected, extending dry season length increased WEOC concentrations by 30% above the 108 μg C/g measured in untreated plots, whereas keeping soils moist prevented WEOC from accumulating. Contrary to our hypothesis, excluding plant litter inputs actually increased WEOC concentrations by 40% above the 105 μg C/g measured in plots with plants. Reducing sugars did not accumulate in dry senesced roots in our laboratory incubation. Potential rates of reducing sugar production by hydrolytic enzymes ranged from 0.7 to 10 μmol·g ·h and far exceeded the rates of reducing sugar accumulation (~0.001 μmol·g ·h ). Our observations do not support the hypothesis that exoenzymes continue to break down litter to produce WEOC in dry soils. Instead, we develop the argument that physical processes are more likely to govern short-term WEOC dynamics via slaking of microaggregates that stabilize SOM and through WEOC redistribution when soils wet up, as well as through less understood effects of drought on the soil mineral matrix.

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Effects of Drought Manipulation on Soil Nitrogen Cycling: A Meta‐Analysis

et al. 2017

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Many regions on Earth are expected to become drier with climate change, which may impact nitrogen (N) cycling rates and availability. We used a meta‐analytical approach on the results of field experiments that reduced precipitation and measured N supply (i.e., indices of N mineralization), soil microbial biomass, inorganic N pools (ammonium (NH4+) and nitrate (NO3−)), and nitrous oxide (N2O) emissions. We hypothesized that N supply and N2O emissions would be relatively insensitive to precipitation reduction and that reducing precipitation would increase extractable NH4+ and NO3− concentrations because microbial processes continue, whereas plant N uptake diminishes with drought. In support of this hypothesis, extractable NH4+ increased by 25% overall with precipitation reduction; NH4+ also increased significantly with increasing magnitude of precipitation reduction. In contrast, N supply and extractable NO3− did not change and N2O emissions decreased with reduced precipitation. Across studies microbial biomass appeared unchanged, yet from the diversity of studies, it was clear that proportionally smaller precipitation reductions increased microbial biomass, whereas larger proportional reductions in rainfall reduced microbial biomass; there was a positive intercept (P = 0.005) and a significant negative slope (P = 0.0002) for the regression of microbial biomass versus % precipitation reduction (LnR = −0.009 × (% precipitation reduction) + 0.4021). Our analyses imply that relative to other N variables, N supply is less sensitive to reduced precipitation, whereas processes producing N2O decline. Drought intensity and duration, through sustained N supply, may control how much N becomes vulnerable to loss via hydrologic and gaseous pathways upon rewetting dry soils.

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Soil carbon and nitrogen dynamics throughout the summer drought in a California annual grassland

Cited by 88 publications

References 77 publications

Gross nitrogen transformation rates in semiarid tropical soils under different salinity and vegetation conditions

Gross nitrogen transformation rates in semiarid tropical soils under different salinity and vegetation conditions

Effects of altered dry season length and plant inputs on soluble soil carbon

Effects of Drought Manipulation on Soil Nitrogen Cycling: A Meta‐Analysis

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