Simple additive simulation overestimates real influence: altered nitrogen and rainfall modulate the effect of warming on soil carbon fluxes.

Experiments and models have led to a consensus that there is positive feedback between carbon (C) fluxes and climate warming. However, the effect of warming may be altered by regional and global changes in nitrogen (N) and rainfall levels, but the current understanding is limited. Through synthesizing global data on soil C pool, input and loss from experiments simulating N deposition, drought and increased precipitation, we quantified the responses of soil C fluxes and equilibrium to the three single factors and their interactions with warming. We found that warming slightly increased the soil C input and loss by 5% and 9%, respectively, but had no significant effect on the soil C pool. Nitrogen deposition alone increased the soil C input (+20%), but the interaction of warming and N deposition greatly increased the soil C input by 49%. Drought alone decreased the soil C input by 17%, while the interaction of warming and drought decreased the soil C input to a greater extent (-22%). Increased precipitation stimulated the soil C input by 15%, but the interaction of warming and increased precipitation had no significant effect on the soil C input. However, the soil C loss was not significantly affected by any of the interactions, although it was constrained by drought (-18%). These results implied that the positive C fluxes-climate warming feedback was modulated by the changing N and rainfall regimes. Further, we found that the additive effects of [warming × N deposition] and [warming × drought] on the soil C input and of [warming × increased precipitation] on the soil C loss were greater than their interactions, suggesting that simple additive simulation using single-factor manipulations may overestimate the effects on soil C fluxes in the real world. Therefore, we propose that more multifactorial experiments should be considered in studying Earth systems.

Effect of ammonia-N and pathogen challenge on complement component 8α and 8ß expression in the darkbarbel catfish Pelteobagrus vachellii.

The complement components C8α and C8ß mediate the formation of the membrane attack complex (MAC) to resist pathogenic bacteria and play important roles in innate immunity. Full-length complement C8α (Pv-C8α) and C8ß (Pv-C8ß) cDNA were identified in the darkbarbel catfish Pelteobagrus vachellii, and their mRNA expression levels were analyzed after ammonia-N and pathogen treatment. The Pv-C8α gene contained 1983 bp, including a 1794-bp open reading frame (ORF) encoding 598 amino acids. The Pv-C8ß gene contained 1952 bp, including a 1761-bp ORF encoding 587 amino acids. Pv-C8α and Pv-C8ß had the highest amino acid identity with rainbow trout Oncorhynchus mykiss C8α (62%) and Japanese flounder Paralichthys olivaceus C8ß (83%), respectively. Sequence analysis indicated that both Pv-C8α and Pv-C8ß contained a thrombospondin type-1 (TSP1) domain, a low-density lipoprotein receptor class A (LDLR-A) domain, a membrane attack complex/perforin (MACPF) domain and an epidermal growth factor-like (EGF-like) domain. In addition, Pv-C8α and Pv-C8ß were mainly distributed in the liver, head kidney, spleen, and eggs. Under ammonia-N stress, the Pv-C8α and Pv-C8ß mRNA levels significantly decreased (P < 0.05), with minimum levels, respectively, attained at 24 and 48 h in the liver, 48 and 24 h in the head kidney, and 24 and 24 h in the spleen. After Aeromonas hydrophila challenge, the Pv-C8α and Pv-C8ß mRNA levels significantly increased (P < 0.05), with maximum levels, respectively, attained at 48 and 24 h in the liver, 24 and 48 h in the head kidney, and 48 and 48 h in the spleen. The present study indicated that Pv-C8α and Pv-C8ß exhibited important immune responses to infection and that ammonia-N in water decreased the immune responses of Pv-C8α and Pv-C8ß.

Effects of pathogenic bacterial challenge after acute sublethal ammonia-N exposure on heat shock protein 70 expression in Botia reevesae.

The objective of this study was to investigate the effects of pathogenic bacterial challenge after acute sublethal ammonia-N exposure on heat shock protein 70 expression in Botia reevesae. After ammonia-N exposure at a constant concentration of 7.21 ± 0.10 mg L(-1) for 96 h, B. reevesae was challenged with Aeromonas hydrophila. Quantitative PCR analysis showed predominant and significant expression of HSP70 in liver, gill, skin, spleen and kidney (P < 0.05), with significantly upregulated expression of the mRNA transcript in these tissues after sublethal ammonia-N exposure and A. hydrophila challenge. Furthermore, following A. hydrophila challenge after ammonia-N exposure, HSP70 mRNA expression was significantly upregulated in kidney and gill tissues, although its expression levels were significantly lower than those detected following A. hydrophila challenge or ammonia-N exposure individually. These results indicate that B. reevesae HSP70 is involved in resistance to pathogenic bacteria. It is hypothesized that ammonia-N results in the downregulation of HSP70 mRNA in immune organs after an A. hydrophila challenge, thus lowering their resistance to pathogenic stress.

[Effects of Fargesia denudata density on its litterfall production, nutrient return, and nutrient use efficiency].

A two-year study on the effects of three densities (D1, 80 +/- 5 stems x m(-2); D2, 140 +/- 8 stems x m(-2); and D3, 220 +/- 11 stems x m(-2)) of Fargesia denudate in a F. denudata--Picea purpurea natural forest on the F. denudate litterfall production, nutrient return, and nutrient use efficiency showed that at the densities of D1, D2 and D3, the annual litterfall production was 793.2, 1135.7 and 1458.5 kg x hm(-2), carbon return was 370.7, 516.2 and 671.5 kg x hm(-2), and the total return of N, P, K, Ca and Mg was 16.3, 22.9 and 29.3 kg x hm(-2), respectively. Ca had the highest return (45%-48% of the total), followed by N (24%-29%), and the lowest were P and Mg (3%-5%), with the sequence of Ca > N > K > Mg and P. The peaks of litterfall production and nutrients return at the three densities were appeared in October (by the end of F. denudate growth season), and another peak at D3 was observed in August. There were no significant differences in the re-allocation of N and K in F. denudate leaves at the three densities, but the P re-allocation and the Ca and Mg accumulation increased with increasing density. The litterfall P use efficiency was the highest and increased with increasing density, implying that P could be a limiting factor for the growth and regeneration of F. denudate.