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Long‐term pedogenesis leads to important changes in the availability of soil nutrients, especially nitrogen (N) and phosphorus (P). Changes in the availability of micronutrients can also occur, but are less well understood. We explored whether changes in leaf nutrient concentrations and resorption were consistent with a shift from N to P limitation of plant productivity with soil age along a > 2‐million‐year dune chronosequence in south‐western Australia. We also compared these traits among plants of contrasting nutrient‐acquisition strategies, focusing on N, P and micronutrients. The range in leaf [P] for individual species along the chronosequence was exceptionally large for both green (103–3000 μg P g⁻¹) and senesced (19–5600 μg P g⁻¹) leaves, almost equalling that found globally. From the youngest to the oldest soil, cover‐weighted mean leaf [P] declined from 1840 to 228 μg P g⁻¹, while P‐resorption efficiency increased from 0% to 79%. All species converged towards a highly conservative P‐use strategy on the oldest soils. Declines in cover‐weighted mean leaf [N] with soil age were less strong than for leaf [P], ranging from 13.4 mg N g⁻¹ on the youngest soil to 9.5 mg N g⁻¹ on the oldest soil. However, mean leaf N‐resorption efficiency was greatest (45%) on the youngest, N‐poor soils. Leaf N:P ratio increased from 8 on the youngest soil to 42 on the oldest soil. Leaf zinc (Zn) concentrations were low across all chronosequence stages, but mean Zn‐resorption efficiency was greatest (55–74%) on the youngest calcareous dunes, reflecting low Zn availability at high pH. N₂‐fixing species had high leaf [N] compared with other species. Non‐mycorrhizal species had very low leaf [P] and accumulated Mn across all soils. We surmise that this reflects Mn solubilization by organic acids released for P acquisition. Synthesis. Our results show community‐wide variation in leaf nutrient concentrations and resorption that is consistent with a shift from N to P limitation during long‐term ecosystem development. High Zn resorption on young calcareous dunes supports the possibility of micronutrient co‐limitation. High leaf [Mn] on older dunes suggests the importance of carboxylate release for P acquisition. Our results show a strong effect of soil nutrient availability on nutrient‐use efficiency and reveal considerable differences among plants of contrasting nutrient‐acquisition strategies.

Summary Ridges of tropical mountains often differ strikingly from neighbouring ravines in terms of forest structure, productivity and species composition. This heterogeneity is poorly understood despite its critical role in biodiversity maintenance, carbon and nutrient budgets. We examined measures of tree biomass and productivity, foliage and litter quality (nutrient concentrations, specific leaf mass, phenolics), herbivory and leaf litter decomposition in each six plots laid out in upper and lower slope position in a tropical montane moist forest in southeastern Ecuador. Productivity, quality of foliage and litter as well as herbivory were significantly lower in upper slope position, and closely correlated with soil nutrient concentrations and accumulated humus. The decomposition of upper slope leaf litter (decomposition rate k) was substantially lower than in litter from lower slope forest, whereas the site of decomposition (slope position) only had a marginal effect on the decomposition rate. Our results suggest that the differences in stand structure, productivity, foliar quality, herbivory and decomposition between slope positions are ultimately due to stronger nutrient limitations in upper slope forest. We propose a general conceptual model that explains origin and maintenance of contrasting forest types along topographical gradients through down‐slope fluxes of nutrients and water, and a nutrient‐driven positive feedback cycle. Lay Summary

Traditionally, crop production in sub-Saharan Africa (SSA) depends primarily on mining soil nutrients. Integrated Soil Fertility Management (ISFM) is an approach for intensifying agriculture in SSA that aims at maximizing the agronomic efficiency (AE) of applied nutrient inputs. ISFM contains the following essential components: proper fertilizer management, use of improved varieties, the combined application of organic inputs and fertilizer, and adaptation of input application rates to within-farm soil fertility gradients where these are important. This paper evaluates, through meta-analysis, the impact of these components on the AE of fertilizer N (N-AE), defined as extra grain yield per kg fertilizer N applied, in maize-based systems in SSA. Since N-AE is low for excessive fertilizer N application rates or when fertilizer is applied on fertile, unresponsive soil, as was confirmed by scatter plots against control yields and fertilizer N application rates, such values were removed from the database in order to focus on and elucidate the more variable and complex responses under less than ideal conditions typical for SSA. Compared with local varieties, the use of hybrid maize varieties significantly increased N-AE values (17 and 26 kg (kg N)⁻¹, respectively) with no differences observed between local and improved, open-pollinated varieties. Mixing fertilizer with manure or compost resulted in the highest N-AE values [36 kg (kg N)⁻¹] while organic inputs of medium quality also showed significantly higher N-AE values compared with the sole fertilizer treatment but only at low organic input application rates (40 and 23 kg (kg N)⁻¹, respectively). High quality organic inputs (Class I) and those with a high C-to-N ratio (Class III) or high lignin content (Class IV) did not affect N-AE values in comparison with the sole fertilizer treatment. Application of N fertilizer on infields resulted in significantly higher N-AE values [31 kg (kg N)⁻¹] compared with the outfields [17 kg (kg N)⁻¹]. The obtained information indicates that N-AE is amenable to improved management practices and that the various components embedded in the ISFM definition result in improvements in N-AE.

Questions Leaf nitrogen (N), phosphorus (P) concentrations and N : P ratio have been extensively studied along environmental gradients, but whether and how leaves and roots show similar responses to climatic and fertility gradients is little studied. Also, the responses of leaf and root N and P in different plant functional types (PFT; legumes, grasses, forbs and shrubs) to environmental gradients are poorly known. We examined the following two hypotheses: (a) P concentration and N : P ratios in leaves or fine roots would not be modulated by soil N for legumes while they would be for non‐legume PFTs; (b) Species turnover would have stronger influence on the responses of N and P concentrations and N : P ratios of plant tissues along aridity and soil fertility gradients than intraspecific variation. Study site Ordos Plateau, China. Methods We collected samples of leaf and fine roots covering 95 species of 28 families across 17 sites affiliated to four vegetation types on the dry Ordos Plateau of North China and compared variations in N and P concentrations and N : P ratios in both leaves and fine roots among PFTs. Results We found that legumes had higher N concentrations in leaves and fine roots than the non‐legume PFTs. Leaf and fine root P and N : P ratios increased with increasing soil N for most non‐legume PFTs, but the relationships were decoupled for legumes. Species turnover had a stronger contribution to these relationships of N and P in leaves and fine roots along aridity and soil N gradients than intraspecific variation. Conclusions When modeling vegetation nutrient stocks and cycling, the predictive power could be improved by taking into account not only influences of soil fertility but also of climate on leaf and root tissue N and soil N on tissue P and N : P ratio, especially for non‐legume functional types. By collecting samples of leaf and fine roots covering 95 species of 28 families across 17 sites affiliated to four vegetation types on the dry Ordos Plateau of North China, we found that N : P ratios in leaf and fine root increased with increasing soil N for non‐legume PFTs, but the relationships were decoupled for legumes due to differences in P limitation.

(edaphic filters drive Myrtaceae assemblages) Aims This study investigated whether soil chemistry act as abiotic drivers of Myrtaceae assemblages, and also investigated the occurrence of indicator species. Methods We first characterize the edaphic conditions of forest fragments occupied by Myrtaceae assemblages in Subtropical Araucaria Forest. Then, we investigated the association between soil chemistry and the structure of the assemblages. Finally, we verified which Myrtaceae species are chemical-edaphic bioindicators. Results We measured 2357 individuals belonging to 26 species from the Myrtaceae family. The Myrtaceae assemblages were predominantly composed by populations with aggregate spatial distribution pattern. This spatial behavior reflects their edaphic requirements because the soil conditions are heterogeneous even on a small scale, forming chemical-edaphic niche patches. Ecological dominance occurred in habitats characterized by restrictive environmental factors such as soils with high acidity and high availability of exchangeable aluminum. Acca sellowiana and Campomanesia xanthocarpa are indicator species of fertile soils, while Myrceugenia regnelliana is acid and low fertility soils indicative. Conclusions In this study we show that soil acidity is an effective driver of Myrtaceae assemblages in Subtropical Araucaria Forest and the use of Myrtaceae indicators can enable policymakers and environmental inspectors to more easily enact conservation in Brazilian ecosystems.

Conservation Agriculture (CA) and Integrated Soil Fertility Management (ISFM) have been promoted in Sub Saharan Africa as a means to improve soil quality. A four season research (March, 2017 to March, 2019) was conducted to evaluate CA-based treatment, no tillage with residue retention (NTR), ISFM-based treatment, conventional tillage with use of manure (CTM), a combination of CA + ISFM, no tillage with residue retention and use of manure (NTRM) and a control, (C) on soil quality attributes. In the two locations (sub-humid and semi-arid) the effect of soil fertility gradients (high and low) were considered. Trials were set out using a one farm one replicate randomized design. In either high or low fertility fields, soil chemical and physical properties were significantly different between the control and NTR, CTM and NTRM with no significant differences between NTR, CTM and NTRM. SOC was higher under NTR and NTRM practices, which consequently had higher hydraulic conductivity, air permeability, mean weight diameter and available phosphorus. For all the treatments and in both locations, the low fertility fields had significantly lower agronomic use efficiency (AUE) compared to the high fertility fields. In both soil types, plant available water capacity and relative water capacity values were below the recommended thresholds indicating low soil water uptake, suboptimal microbial activity and consequently low nutrient uptake which explains the observed low AUE.

We propose an operational definition of soil “fertility” that is applicable to plant community ecology and develop a method of measuring and quantifying it, using structural equations modeling, that is generalizable to soils in different regions whose fertility has different causes. To do this, we used structural equation modeling (SEM). The measurement submodel predicts the latent “generalized fertility,” F G, of a soil using four indicator variables: the relative growth rates of Festuca rubra, Trifolium pratense, Triticum aestivum, and Arabidopsis thaliana. The direct causes of F G in this study were the supply rates of NO3 − , P, and K as well as three indirect causes consisting of three physical soil properties, but these can change between studies. The model was calibrated using 76 grassland soils from southern Quebec, Canada and independently tested using aboveground net primary productivity (NPP) of the natural vegetation over two growing seasons. Both the measurement submodel and the full SEM fit the data well. The F G values predicted 51% of the variance in NPP and were a better predictor than any other single variable, including the actual nutrient flux rates. Furthermore, this model can be applied to grassland soils anywhere because of its modular nature in which the causes and effects of soil fertility are clearly separated.

BACKGROUND AND AIMS: A soil fertility gradient, ranging from infertile to highly fertile soils, may define whether or not a plant will establish and spread at a site. We evaluated whether or not such a fertility gradient exists for Rosa multiflora Thunb., a nonnative invasive shrub, and Kalmia latifolia L., a native problem shrub, in closed-canopy forests of the eastern U.S. METHODS: We sampled soil and vegetation at the regional scale, along four randomly located 1-km transects in 70+ year-old undisturbed forests in each of three national forests in Ohio, Pennsylvania and West Virginia. We also sampled soil, vegetation and leaf tissue at the local scale, from ten individual shrubs of each species in each national forest. RESULTS: Regional analyses showed a significant fertility gradient with Ohio being the most fertile and West Virginia the least. Soil fertility was associated with pH (most acidic in West Virginia and least acidic in Ohio) and elevation (highest in West Virginia and lowest in Ohio). At the local level, R. multiflora was associated with soil Ca:Al ratios greater than 0.5, and K. latifolia was associated with Ca:Al ratios less than 0.3. Rosa multiflora foliage contained higher concentrations of Ca, Mg, and K than K. latifolia, while K. latifolia foliage contained higher concentrations of Mn and Zn. CONCLUSIONS: Our research documents the importance of soil fertility as a predictor of the establishment of invasive and expansive shrubs. This study further shows that R. multiflora can establish and spread across a broader range of soil conditions than K. latifolia.

Decline in soil fertility is a major threat to land productivity and food security in the East African highlands. This calls for the application of nutrient inputs to improve crop productivity. A study was conducted in Nyabihu District of Rwanda from 2013 to 2016 to assess the effect of Alnus acuminata green manure (AGM)─applied in situ, through biomass alone, or combined with inorganic fertilizer─on the productivity and profitability of maize (Zea mays), beans (Phaseolus vulgaris), and potato (Solanum tuberosum). The treatments included application of AGM, inorganic fertilizer, combination of AGM and inorganic fertilizer, and unfertilized plot as a control (except for potato). These treatments were compared in two seasons and on two local soil fertility levels (medium and high) as defined by the farmer’s knowledge and experience. There was a convergence between farmers’ criteria and soil analysis in the soil fertility evaluation. Crops yields were analyzed using a linear mixed model while for other parameters, descriptive statistics were applied. The combination of AGM and inorganic fertilizer recorded the highest increment in maize (44%) and bean (46%) yields compared with inorganic fertilizer while it increased up to 87% compared with the unfertilized control. The financial analysis showed that AGM + inorganic fertilizer recorded the highest value-to-cost ratio (VCR) of 24.6 for potato and a significantly lower VCR (2.9) for maize and beans. The high VCR highlights a significant potential contribution of AGM + inorganic fertilizer to increase incomes of resource-constrained potato farmers in the Rwandan highlands. However, low crop prices possibly make this practice less attractive for those cultivating maize and beans.

The need to promote fertiliser use by African smallholder farmers to counteract the current decline in per capita food production is widely recognised. But soil heterogeneity results in variable responses of crops to fertilisers within single farms. We used existing databases on maize production under farmer (F-M) and researcher management (R-M) to analyse the effect of soil heterogeneity on the different components of nutrient use efficiency by maize growing on smallholder farms in western Kenya: nutrient availability, capture and conversion efficiencies and crop biomass partitioning. Subsequently, we used the simple model QUEFTS to calculate nutrient recovery efficiencies from the R-M plots and to calculate attainable yields with and without fertilisers based on measured soil properties across heterogeneous farms. The yield gap of maize between F-M and R-M varied from 0.5 to 3 t grain ha−1 season−1 across field types and localities. Poor fields under R-M yielded better than F-M, even without fertilisers. Such differences, of up to 1.1 t ha−1 greater yields under R-M conditions are attributable to improved agronomic management and germplasm. The relative response of maize to N–P–K fertilisers tended to decrease with increasing soil quality (soil C and extractable P), from a maximum of 4.4-fold to −0.5-fold relative to the control. Soil heterogeneity affected resource use efficiencies mainly through effects on the efficiency of resource capture. Apparent recovery efficiencies varied between 0 and 70% for N, 0 and 15% for P, and 0 to 52% for K. Resource conversion efficiencies were less variable across fields and localities, with average values of 97 kg DM kg−1 N, 558 kg DM kg−1 P and 111 kg DM kg−1 K taken up. Using measured soil chemical properties QUEFTS over-estimated observed yields under F-M, indicating that variable crop performance within and across farms cannot be ascribed solely to soil nutrient availability. For the R-M plots QUEFTS predicted positive crop responses to application of 30 kg P ha−1 and 30 kg P ha−1 + 90 kg N ha−1 for a wide range of soil qualities, indicating that there is room to improve current crop productivity through fertiliser use. To ensure their efficient use in sub-Saharan Africa mineral fertilisers should be: (1) targeted to specific niches of soil fertility within heterogeneous farms; and (2) go hand-in-hand with the implementation of agronomic measures to improve their capture and utilisation