Nitrogen and phosphorous dynamics with stand development of Pinus massoniana plantations in Southeast China

INTRODUCTION

Nutrient resorption is a key mechanism to conserve nutrients and overcome nutrient limitation in perennial plants. As an important afforested tree species in subtropical regions, Pinus massoniana grows well in nutrient-poor environments, however, the age-related pattern of nutrient acquisition strategy and the underlying mechanisms in P. massoniana plantations remain unclear.

METHODS

In this study, concentrations of nitrogen (N) and phosphorus (P) were measured in green and senesced needles, roots and soil samples collected from P. massoniana plantations with different stand ages (9-, 17-, 26-, 34- and 43-year-old) in south China. From these samples, nutrient resorption efficiency (RE) and stoichiometry were calculated.

RESULTS

Needle PRE significantly decreased with stand age, while there was no clear pattern of NRE along the stand development. Green needle N:P in older stands was significantly lower than in younger ones. Senesced needle C:P and N:P significantly decreased with stand age. Root and soil available P concentrations were significantly higher in older stands than in younger ones, and PRE was negatively correlated with soil available P concentration.

DISCUSSION

There was a shift from "conservative consumption" to "resource spending" P-use strategy, and P limitation decreased with stand development of P. massoniana plantations. The results provide information of changes in nutrients dynamics, which is relevant for the sustainable management of subtropical forest plantations.

Dynamics of Leaf-Litter Biomass, Nutrient Resorption Efficiency and Decomposition in a Moso Bamboo Forest After Strip Clearcutting

Strip clearcutting can significantly reduce the harvesting costs of moso bamboo forests. Although bamboo is characterized by rapid accumulation of biomass, it is still a concern that this management method may reduce long-term productivity. Nutrient cycling has long been considered essential for forests to maintain high primary productivity. However, nutrient cycling of bamboo forests after strip cutting has not been previously reported. We conducted a strip clearcutting experiment and surveyed the litter dynamics for 1 year. We assessed changes in litter nutrients in response to the cutting and calculated the nutrient resorption efficiency and litter decomposition rate to evaluate the effect on nutrient use efficiency and nutrient return. Our results showed that strip cutting had no significant effect on litter production and nutrient return in the moso bamboo forest (p > 0.05). However, annual litter biomass and nutrient return in reserved belts (RB) were significantly higher than those in the control (CK) (p < 0.05). P and K resorption efficiencies in RB were significantly higher than in CK during certain periods of bamboo growth (p < 0.05). We also observed that the annual decay constant of CK was significantly higher than that of plots that were strip clearcut (SC) (p < 0.05). Our results suggest that strip cutting does not affect nutrient use efficiency or storage in the short term.

Biochar Amendment Alters the Nutrient-Use Strategy of Moso Bamboo Under N Additions

Nutrient resorption can affect plant growth, litter decomposition, and nutrient cycling. Although the effects of nitrogen (N) and biochar fertilizers on soil nutrient concentrations and plant nutrient uptake have been studied, an understanding of how combined applications of N and biochar affect plant nutrient resorption in plantations is lacking. In this study, we applied N (0, 30, 60, and 90 kg N ha^-1 yr^-1 defined as N0, N30, N60, and N90, respectively) and biochar (0, 20, and 40 t biochar ha^-1 defined as BC0, BC20, and BC40, respectively) to the soil of a Moso bamboo plantation. We investigated the effects of these treatments on N and phosphorus (P) resorption by young and mature bamboo plants, as well as the relationships between nutrient resorption and leaf and soil nutrient concentrations. Young bamboo showed significantly greater foliar N resorption efficiency (NRE) and P resorption efficiency (PRE) than mature bamboo. N addition alone significantly increased the N resorption proficiency (NRP) and P resorption proficiency (PRP) but significantly decreased the NRE and PRE of both young and mature bamboo. In both the N-free and N-addition treatments, biochar amendments significantly reduced the foliar NRE and PRE of young bamboo but had the opposite effect on mature bamboo. Foliar NRE and PRE were significantly negatively correlated with fresh leaf N and P concentrations and soil total P concentration but significantly positively correlated with soil pH. Our findings suggest that N addition inhibits plant nutrient resorption and alters the nutrient-use strategy of young and mature bamboo from "conservative consumption" to "resource spending." Furthermore, biochar amendment enhanced the negative effect of N addition on nutrient resorption in young bamboo but reduced the negative effect on that of mature bamboo under N-addition treatments. This study provides new insights into the combined effects of N and biochar on the nutrient resorption of Moso bamboo and may assist in improving fertilization strategies in Moso bamboo plantations.

Simulated climate change decreases nutrient resorption from senescing leaves

Nutrient resorption is the process whereby plants recover nutrients from senescing leaves and reallocate them to storage structures or newer tissues. Elemental resorption of foliar N and P has been shown to respond to temperature and precipitation, but we know remarkably little about the influence of warming and drought on the resorption of these and other essential plant macro- and micronutrients, which could alter the ability of species to recycle their nutrients. We conducted a 5 year manipulative field study to simulate predicted climate change conditions and studied the effects of warming (W), rainfall reduction (RR), and their combination (W+RR) on nutrient resorption efficiency in five coexisting shrub species in a semiarid shrubland. Both mature and senesced leaves showed significant reductions in their nutrient contents and an altered stoichiometry in response to climate change conditions. Warming (W, W+RR) reduced mature leaf N, K, Ca, S, Fe, and Zn and senesced leaf N, Ca, Mg, S, Fe, and Zn contents relative to ambient temperature conditions. Warming increased mature leaf C/N ratios and decreased N/P and C/P ratios and increased senesced leaf C/N and C/P ratios. Furthermore, W and W+RR reduced nutrient resorption efficiencies for N (6.3%), K (19.8%), S (70.9%) and increased Ca and Fe accumulation in senesced leaves (440% and 35.7%, respectively) relative to the control treatment. Rainfall reduction decreased the resorption efficiencies of N (6.7%), S (51%), and Zn (46%). Reductions in nutrient resorption efficiencies with warming and/or rainfall reduction were rather uniform and consistent across species. The negative impacts of warming and rainfall reduction on foliar nutrient resorption efficiency will likely cause an impairment of plant nutrient budgets and fitness across coexisting native shrubs in this nutrient-poor habitat, with probable implications for key ecosystem functions such as reductions in nutrient retention in vegetation, litter decomposition, and nutrient cycling rates.

Does Plant Size Influence Leaf Elements in an Arborescent Cycad?

Plant size influences the leaf nutrient relations of many species, but no cycad species has been studied in this regard. We used the arborescent Cycas micronesica K.D. Hill to quantify leaf nutrient concentrations of trees with stems up to 5.5-m in height to determine if height influenced leaf nutrients. Green leaves were sampled in a karst, alkaline habitat in Rota and a schist, acid habitat in Yap. Additionally, senesced leaves were collected from the trees in Yap. Minerals and metals were quantified in the leaf samples and regressed onto stem height. Green leaf nitrogen, calcium, manganese, and iron decreased linearly with increased stem height. Senesced leaf carbon, iron, and copper decreased and senesced leaf nitrogen increased with stem height. Nitrogen resorption efficiency decreased with stem height. Phosphorus and potassium resorption efficiencies were not influenced by plant size, but were greater than expected based on available published information. The results indicate leaf nutrient concentrations of this cycad species are directly influenced by plant size, and illuminate the need for adding more cycad species to this research agenda. Plant size should be measured and reported in all cycad reports that include measurements of leaf behavior.

Inserting cycads into global nutrient relations data sets

Global research agendas on plant nutrient relations attempt to illuminate biotic and abiotic factors that mediate nutrient relations. We contend that cycad species are not adequately represented in these global agendas. Little is known about how various cycad traits such as phylogenetics, growth form, latitudinal range, or ecological niche influence concentration, stoichiometry, and resorption dynamics of leaf nutrients. The addition of cycad species data to the global research dataset will address a critical knowledge gap and benefit global research needs to improve our systemic understanding of biotic and abiotic influences on plant nutrition.

Leaf Damage by Phytophagous Beetles alters Terminalia catappa Green and Senesced Leaf Chemistry

Chemical traits of Terminalia catappa L. leaves were determined on the island of Guam to understand the changes caused by beetle leaf herbivory. Green leaf chemistry indicated nitrogen was the most limiting nutrient in the climate and soils of Guam. The changes in leaf chemistry following beetle damage were extensive. Senesced leaf chemistry indicated beetle damage decreased some traits that predict lower leaf litter quality, such as lignin, but also decreased some traits that predict higher leaf litter quality, such as nitrogen. The stoichiometric traits based on carbon:macronutrient and lignin:macronutrient generally predicted higher quality leaf litter following beetle herbivory. The beetles that produce this form of T. catappa leaf damage on Guam are non-native, and overall, the results indicate these pests will increase the rate of litter decomposition and nutrient turnover in habitats where T. catappa is prevalent.

Stoichiometric and nutrient resorption characteristics of dominant tree species in subtropical Chinese forests

This study investigated seasonal patterns in stoichiometric ratios, nutrient resorption characteristics, and nutrient use strategies of dominant tree species at three successional stages in subtropical China, which have not been fully understood. Fresh leaf and leaf litterfall samples were collected in growing and nongrowing seasons for determining the concentrations of carbon (C), nitrogen (N), and phosphorus (P). Then, stoichiometric ratios (i.e., C:N, C:P, N:P, and C:N:P) and resorption parameters were calculated. Our results found that there was no consistent variation in leaf C:N and C:P ratios among different species. However, leaf N:P ratios in late-successional species became significantly higher, indicating that P limitation increases during successional development. Due to the P limitation in this study area, P resorption efficiency and proficiency were higher than corresponding N resorption parameters. Dominant tree species at early-successional stage adopted "conservative consumption" nutrient use strategy, whereas the species at late-successional stage inclined to adopt "resource spending" strategy.

Combined effects of nitrogen addition and litter manipulation on nutrient resorption of Leymus chinensis in a semi-arid grassland of northern China

Plant growth in semi-arid ecosystems is usually severely limited by soil nutrient availability. Alleviation of these resource stresses by fertiliser application and aboveground litter input may affect plant internal nutrient cycling in such regions. We conducted a 4-year field experiment to investigate the effects of nitrogen (N) addition (10 g N·m(-2) ·year(-1)) and plant litter manipulation on nutrient resorption of Leymus chinensis, the dominant native grass in a semi-arid grassland in northern China. Although N addition had no clear effects on N and phosphorus (P) resorption efficiencies in leaves and culms, N fertilisation generally decreased leaf N resorption proficiency by 54%, culm N resorption proficiency by 65%. Moreover, N fertilisation increased leaf P resorption proficiency by 13%, culm P resorption proficiency by 20%. Under ambient or enriched N conditions, litter addition reduced N and P resorption proficiencies in both leaves and culms. The response of P resorption proficiency to litter manipulation was more sensitive than N resorption proficiency: P resorption proficiency in leaves and culms decreased strongly with increasing litter amount under both ambient and enriched N conditions. In contrast, N resorption proficiency was not significantly affected by litter addition, except for leaf N resorption proficiency under ambient N conditions. Furthermore, although litter addition caused a general decrease of leaf and culm nutrient resorption efficiencies under both ambient and enriched N conditions, litter addition effects on nutrient resorption efficiency were much weaker than the effects of litter addition on nutrient resorption proficiency. Taken together, our results show that leaf and non-leaf organs of L. chinensis respond consistently to altered soil N availability. Our study confirms the strong effects of N addition on plant nutrient resorption processes and the potential role of aboveground litter, the most important natural fertiliser in terrestrial ecosystems, in influencing plant internal nutrient cycling.

Concentrations and resorption patterns of 13 nutrients in different plant functional types in the karst region of south-western China

BACKGROUND AND AIMS

Elucidating the stoichiometry and resorption patterns of multiple nutrients is an essential requirement for a holistic understanding of plant nutrition and biogeochemical cycling. However, most studies have focused on nitrogen (N) and phosphorus (P), and largely ignored other nutrients. The current study aimed to determine relationships between resorption patterns and leaf nutrient status for 13 nutrient elements in a karst vegetation region.

METHODS

Plant and soil samples were collected from four vegetation types in the karst region of south-western China and divided into eight plant functional types. Samples of newly expanded and recently senesced leaves were analysed to determine concentrations of boron (B), calcium (Ca), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), molybdenum (Mo), N, sodium (Na), P, sulphur (S) and zinc (Zn).

KEY RESULTS

Nutrient concentrations of the karst plants were lower than those normally found in other regions of China and the rest of the world, and plant growth was mainly limited by P. Overall, four nutrients revealed resorption [N (resorption efficiency 34·6 %), P (48·4 %), K (63·2 %) and Mg (13·2 %)], seven nutrients [B (-16·1 %), Ca (-44·0 %), Cu (-14·5 %), Fe (-205·5 %), Mn (-72·5 %), Mo (-35·6 %) and Zn (-184·3 %)] showed accumulation in senesced leaves and two nutrients (Na and S) showed no resorption or accumulation. Resorption efficiencies of K and Mg and accumulation of B, Ca, Fe and Mn differed among plant functional types, and this strongly affected litter quality. Resorption efficiencies of N, P and K and accumulation of Ca and Zn increased with decreasing concentrations of these nutrients in green leaves. The N:P, N:K and N:Mg ratios in green leaves predicted resorption proficiency for N, K and Mg, respectively.

CONCLUSIONS

The results emphasize the fact that nutrient resorption patterns strongly depend on element and plant functional type, which provides new insights into plant nutrient use strategies and nutrient cycling in karst ecosystems.

Seasonal branch nutrient dynamics in two Mediterranean woody shrubs with contrasted phenology

BACKGROUND AND AIMS

Mediterranean woody plants have a wide variety of phenological strategies. Some authors have classified the Mediterranean phanaerophytes into two broad phenological categories: phenophase-overlappers (that overlap resource-demanding activities in a short period of the year) and phenophase-sequencers (that protract resource-demanding activities throughout the year). In this work the impact of both phenological strategies on leaf nutrient accumulation and retranslocation dynamics at the level of leaves and branches was evaluated. Phenophase-overlappers were expected to accumulate nutrients in leaves throughout most of the year and withdraw them efficiently in a short period. Phenophase-sequencers were expected to withdraw nutrients progressively throughout the year, without long accumulation periods.

METHODS

To test this hypothesis, variations in phenology and leaf NPK in the crown of a phenophase-overlapper Cistus laurifolius and a phenophase-sequencer Bupleurum fruticosum were monitored monthly during 2 years.

KEY RESULTS

Changes in nutrient concentration at the leaf level were not clearly related with the different phenologies. Nitrogen and phosphorous resorption efficiencies were lower in the phenophase-overlapper, and accumulation-retranslocation seasonality was similar in both species. Changes in the branch nutrient pool agreed with the hypothesis that the phenophase-overlapper accumulated nutrients from summer until the bud burst of the following spring, recovering a large nutrient pool during massive leaf shedding. The phenophase-sequencer did not accumulate nutrients from autumn until early spring, achieving lower nutrient recovery during spring leaf shedding.

CONCLUSIONS

It is concluded that phenological demands influence branch nutrient cycling. This effect is easier to detect by assessing changes in the branch nutrient pool rather than changes in the leaf nutrient concentration.