| 1. |
- Wang, Shuang, et al.
(författare)
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Microbial formation and stabilisation of soil organic carbon is regulated by carbon substrate identity and mineral composition
- 2022
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 414
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Tidskriftsartikel (refereegranskat)abstract
- The view that soil organic C (SOC) is formed mainly from non-metabolised and recalcitrant organic residues is being challenged by an emerging view that metabolic by-products form more stable associations with soil minerals. However, the effects of C substrate identity and soil mineral composition (and interactions) on microbial physiology and SOC formation are still not well understood. We added contrasting substrates (glucose, alanine and a mixture of glucose, alanine, and oxalic acid) into artificial soils of varying mineral composition (montmorillonite, kaolinite, and kaolinite plus goethite and hematite) for 12 weeks. We found that glucose led to 1.45 and 1.75 times more SOC formation than alanine and the mixed substrate, respectively. Montmorillonite based soils gained approximately 1.3 times more SOC compared to the other two soils. Compared with kaolinite-only soils, the inclusion of goethite and hematite had a positive effect on total SOC, extracellular C and biologically stable C when amended with alanine, but a negative effect on these SOC fractions when amended with glucose. Soils with greater SOC formation were associated with high microbial C use efficiency (CUE) and extracellular C, suggesting that spatial allocation by the microbial biomass is pivotal for creating stable SOC. Fungi-dominated soils typically had a higher CUE, which was positively correlated with the formation of new SOC. These results suggest that the identity of plant inputs will have a strong bearing on the formation of SOC via interactions with the soil microbial community and soil mineralogy.
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| 2. |
- Zhang, Peng, et al.
(författare)
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The influence of elevational differences in absolute maximum density values on regional climate reconstructions
- 2015
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Ingår i: Trees-Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890. ; 29:4, s. 1259-1271
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Tidskriftsartikel (refereegranskat)abstract
- We found that indiscriminately using tree-ring MXD data with inhomogeneous temporal distribution from different elevations might cause biased chronologies. A mean-adjusting method was developed to overcome this bias. Here we analyse maximum latewood density (MXD) of Pinus sylvestris L. (Scots pine), from deadwood (dry) and subfossil wood (from lakes) collected along an elevation gradient in and close to the central Scandinavian Mountains, in the province of Jamtland, Sweden. Focusing on two common time periods (900-1150 CE and 1300-1550 CE), the mean absolute MXD of deadwood samples showed an inverse relationship with elevation, i.e. the absolute MXD decreases with elevation. However, the MXD values of the subfossil samples did not show such a consistent relationship with elevation. It was also noted that the differences in mean absolute MXD values among sites of different elevations in a given period were larger than among sites of similar elevation between the two time periods, where the former was assumed to be warmer than the latter. Using a theoretical model and a real example, it was shown that indiscriminately using MXD data with inhomogeneous temporal distribution from different elevations may cause biased chronologies, which can have significant effects on subsequent interpretations of past climate variability. A mean-adjusting method was developed to overcome this bias, and its usefulness was demonstrated by comparing two chronologies built on mean-adjusted and unadjusted MXD samples. It was concluded that unadjusted samples from different elevations with inhomogeneous temporal distribution can distort the long-term trend in a final chronology, while this bias can be alleviated if mean-adjusted samples are used.
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