Intra-annual variation of soil respiration across four heterogeneous longleaf pine forests in the southeastern United States

Abstract

Soil respiration (R S) is one of the largest fluxes of net ecosystem exchange and is related to both soil climate and vegetatively driven substrate supply at various spatial and temporal scales. Relationships between the intra-annual variation in R S and abiotic and biotic variables were examined across diverse longleaf pine (Pinus palustris Mill.) forests to better understand factors related to R S in these low density, spatially heterogeneous forests. Soil respiration, soil temperature, soil moisture, litter mass, size and proximity of nearby trees, understory cover, and root biomass were measured over 13 months in four longleaf pine forests varying in age from 5 to 87 years. The exponential relationship between R S and soil temperature accounted for the majority of the intra-annual variation in R S with a corresponding temperature sensitivity (Q 10) of 2.18. Soil moisture affected the R S-temperature relationship by dampening R S and Q 10 during times of extremely dry soil conditions, as defined by soil moisture ≤ 50 % of the texture-derived wilting point, but volumetric soil moisture did not directly correlate with R S. The intra-annual variation in temperature-normalized R S was negatively related to the distance to nearest tree and positively related to pine root biomass, but not related to litter mass, understory cover, or stand structural variables such as stand age, basal area, or tree density. Annual R S estimates ranged from 12.0 Mg ha −1 of C in the 5-year-old stand with mostly grass stage seedlings to 13.9 Mg ha −1 of C in the dense 21-year-old stand. This study contributes to our understanding of carbon fluxes across diverse longleaf pine ecosystems and indicates the importance of climate in determining the carbon sink potential of southeastern longleaf pine forests.

Effect of Cultivar on Chlorophyll Meter and Canopy Reflectance Measurements in Cucumber

“…To compare the effect of cultivar on the relationship between leaf N content and optical sensor measurement, the methodology used by ArchMiller et al [43] was used. Firstly, the relationship between leaf N content and optical sensor measurement for the three cultivars together was established, for chlorophyll and canopy reflectance sensor measurements.…”

Partitioning Longleaf Pine Soil Respiration into Its Heterotrophic and Autotrophic Components through Root Exclusion

“…Subke et al [7] and others [29,30] found that the proportion of R h to R s varies with annual R s levels. To make a comparison to Subke et al [7], we assumed that annual R s from these longleaf pine stands was similar to those measured in other nearby longleaf pine stands varying in age and structure (12 to 14 Mg¨C¨ha´1¨year´1) [31]. Our range in R h to R s corrected for root decay is comparable to the mean ratio of R h to R s (60%˘12%) from Subke et al [7] across similar temperate coniferous ecosystems with annual R s from 12 to 14 Mg¨C¨ha´1¨year´1.…”

Effect of Heavy Machine Traffic on Soil CO2 Concentration and Efflux in a Pinus koraiensis Thinning Stand

“…The covariance structures of regression Equation ( 6) was chosen by minimizing the corrected Akaike information criteria (AICC) [26].…”

“…Therefore, the response of soil respiration to temperature is generally estimated by the temperature coefficient (Q 10 ) [24]; the global median Q 10 of soil respiration has been reported to be 2.4 [21]. However, Q 10 values can vary as per forest type and climatic conditions [24][25][26]. In addition, SWC alters oxygen diffusivity, which indirectly affects soil respiration in compacted soils [13,23].…”