Effects of nitrogen loading under low and high phosphorus conditions on above- and below-ground growth of hybrid larch F1 seedlings

Abstract

(4)Under present environmental conditions, hybrid larch F1 (Larix gmelinii var. japonica × Larix kaempferi) is a promising afforestation species as it has a high growth rate and tolerance against grazing damage, disease and cold. However, the input of nitrogen (N) to forests due to the increase of anthropogenic N is causing imbalances of N compared to other nutrients, especially phosphorus (P), thus affecting the root growth of healthy seedlings. However, knowledge on how different N and P conditions affect F1 root growth is still limited. In this study, various N (3 levels) and P (no addition and addition) conditions were imposed to investigate the effect of N loading on larch F1 seedlings under different P conditions. Needle N: P ratio, aboveground growth, belowground growth as well as fine root production were measured. The results showed that needle N: P ratio was higher under low P loading, and aboveground growth of seedlings increased with N loading at both low and high P conditions. Relative fine root production was decreased by N loading. On the other hand, fine root to total dry proportion was increased by N loading at no P addition, suggesting that limited P availability could increase fine root production. Total root proportion to total dry mass was decreased by N loading at both P conditions. We concluded that N loading has different effects on above-and below-ground growth of larch F1 and its effects may also differ according to P conditions, indicating that both N and P conditions should be carefully considered when planting hybrid larch F1.

Fast-growing Larix kaempferi suffers under nutrient imbalance caused by phosphorus fertilization in larch plantation soil

“…3 A), as previously proposed by Reich et al (1994). Decreased foliar N concentrations have been detected under P fertilization also in L. kaempferi (L. leptolepis in van Goor, 1953), Rhizophora mangle (Lovelock et al, 2004), four dominant savannah woody species (Bucci et al, 2006) and larch hybrid seedlings (Fujita et al, 2018). However, the reason for this phenomenon is not clear, but it may be caused by the response of water relations and hydraulic architecture to N or P addition (Goldstein et al, 2013).…”

Evaluating Soil–Root Interaction of Hybrid Larch Seedlings Planted under Soil Compaction and Nitrogen Loading

“…N loading promoted root development, especially under soil compaction. N loading increased fine root density and its proportion under soil compaction, which might be associated with high susceptibility to drought [43]. Indeed, a significant interaction effect of soil compaction and N loading was observed on current-year growth parameters ( Table 1).…”

“…Further, the effects of N loading were not significant on the relationship between HCI and root traits (Table S5), which could be supported by the persistent relationship between roots and soil physical parameters under N application [50]. Soil recovery induced by root development of planted F 1 might not be associated with soil N condition, even though N loading increased lateral and fine root proportions [42,43]. Possible reasons for the persistent relationship between root development and soil recovery could be linked to more specific root morphological responses to soil compaction and N loading.…”

“…The effects of N loading on tree growth and the symbiosis between ectomycorrhizal (ECM) fungi have been extensively investigated [40,41]. N loading promotes the growth of F 1 seedling [42], whereas excess N loading would reduce its stress resistance [43]. A stable ECM community of F 1 seedlings was observed under N loading [41].…”

“…In this study, we investigated the growth of F 1 seedlings planted in the compacted soil where N was added. Given the root response to soil physical [31] and nutritional conditions [43], we hypothesized that N loading would increase the fine root proportion of F 1 seedlings under soil compaction, resulting in a reduced effect of root development on soil recovery. We attempted to verify the following objectives: (1) whether the root developments of F 1 would affect soil hardness and (2) how the morphological traits respond to soil compaction and N loading.…”