Although a significant amount of the organic C stored in soil resides in subsurface horizons, the dynamics of subsurface C stores are not well understood. The objective of this study was to determine if changes in soil moisture, temperature, and nutrient levels have similar effects on the mineralization of surface (0–25 cm) and subsurface (below 25 cm) C stores. Samples were collected from a 2 m deep unsaturated mollisol profile located near Santa Barbara, CA, USA. In a series of experiments, we measured the influence of nutrient additions (N and P), soil temperature (10–35°C), and soil water potential (−0.5 to −10 MPa) on the microbial mineralization of native soil organic C. Surface and subsurface soils were slightly different with respect to the effects of water potential on microbial CO2 production; C mineralization rates in surface soils were more affected by conditions of moderate drought than rates in subsurface soils. With respect to the effects of soil temperature and nutrient levels on C mineralization rates, subsurface horizons were significantly more sensitive to increases in temperature or nutrient availability than surface horizons. The mean Q10 value for C mineralization rates was 3.0 in surface horizons and 3.9 in subsurface horizons. The addition of either N or P had negligible effects on microbial CO2 production in surface soil layers; in the subsurface horizons, the addition of either N or P increased CO2 production by up to 450% relative to the control. The results of these experiments suggest that alterations of the soil environment may have different effects on CO2 production through the profile and that the mineralization of subsurface C stores may be particularly susceptible to increases in temperature or nutrient inputs to soil.

Increases in tree biomass may be an important sink for CO 2 as the atmospheric concentration continues to increase. Tree growth in temperate forests is often limited by the availability of soil nutrients. To assess whether soil nutrient limitation will constrain forest productivity under high atmospheric CO 2 , we studied the changes in forest litter production and nutrient cycling in a maturing southern U.S. loblolly pine-hardwood forest during two years of free-air CO 2 enrichment. The objective of this paper is to present data on the chemistry of green leaves and leaf litter, nutrient-retranslocation efficiency, aboveground litter production, whole-system nutrient-use efficiency, decomposition, and N availability in response to forest growth under elevated CO 2 .The chemical composition of green leaves and leaf litter was largely unaffected by elevated CO 2 . Green-leaf nitrogen (N) and phosphorus (P) concentrations were not significantly lower under elevated CO 2 . N and P retranslocation from green leaves did not increase under elevated CO 2 ; therefore, leaf litter N and P concentrations were not significantly lower under elevated CO 2 . The concentrations of carbon, lignin, and total nonstructural carbohydrates in litter were not significantly different under elevated CO 2 .Total aboveground litterfall increased significantly with CO 2 fumigation. The increase in litterfall was due to significant increases in loblolly pine leaf litter and bark production. The mass of leaves from deciduous species did not increase with CO 2 fumigation. Wholesystem nutrient-use efficiency (aboveground litterfall/nutrient content of litterfall) did not increase as a consequence of forest growth under elevated CO 2 , but N and P fluxes from vegetation to the forest floor increased significantly. During the second year of CO 2 fumigation, the flux of N and P to the forest floor in litterfall increased by 20% and 34%, respectively.The rate of mass loss during one year of decomposition was unaffected by ''litter type'' (whether the litter was produced under ambient or elevated CO 2 ), nor by the ''site'' of decomposition (whether the litter was decomposed in the ambient or elevated CO 2 plots). N was immobilized in litter during decomposition, whereas P was mineralized. There was no consistent effect of litter type or site on nutrient dynamics in decomposing litter.There was no significant effect of elevated CO 2 on the pool size of inorganic N (NH 4 ϩ and NO 3 Ϫ ) in the top 7.5 cm of mineral soil. The rate of net N mineralization and nitrification in mineral soil was not significantly different between treatment and control plots.Identifying the source of the nutrients lost in litterfall is critical to the long-term potential growth stimulation of forests under elevated CO 2 . If the nutrients lost from biomass come from storage (e.g., the movement of nutrients from wood to leaves), then the increase in litter production should decrease over time as slowly replenished nutrient reserves are exhausted. If the nutrients lost in pl...

Objective Voltage‐gated sodium channels (SCNs) share similar amino acid sequence, structure, and function. Genetic variants in the four human brain‐expressed SCN genes SCN1A/2A/3A/8A have been associated with heterogeneous epilepsy phenotypes and neurodevelopmental disorders. To better understand the biology of seizure susceptibility in SCN‐related epilepsies, our aim was to determine similarities and differences between sodium channel disorders, allowing us to develop a broader perspective on precision treatment than on an individual gene level alone. Methods We analyzed genotype‐phenotype correlations in large SCN‐patient cohorts and applied variant constraint analysis to identify severe sodium channel disease. We examined temporal patterns of human SCN expression and correlated functional data from in vitro studies with clinical phenotypes across different sodium channel disorders. Results Comparing 865 epilepsy patients (504 SCN1A, 140 SCN2A, 171 SCN8A, four SCN3A, 46 copy number variation [CNV] cases) and analysis of 114 functional studies allowed us to identify common patterns of presentation. All four epilepsy‐associated SCN genes demonstrated significant constraint in both protein truncating and missense variation when compared to other SCN genes. We observed that age at seizure onset is related to SCN gene expression over time. Individuals with gain‐of‐function SCN2A/3A/8A missense variants or CNV duplications share similar characteristics, most frequently present with early onset epilepsy (<3 months), and demonstrate good response to sodium channel blockers (SCBs). Direct comparison of corresponding SCN variants across different SCN subtypes illustrates that the functional effects of variants in corresponding channel locations are similar; however, their clinical manifestation differs, depending on their role in different types of neurons in which they are expressed. Significance Variant function and location within one channel can serve as a surrogate for variant effects across related sodium channels. Taking a broader view on precision treatment suggests that in those patients with a suspected underlying genetic epilepsy presenting with neonatal or early onset seizures (<3 months), SCBs should be considered.

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