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• There are two theories about how allocation of metabolic products occurs. The allometric biomass partitioning theory (APT) suggests that all plants follow common allometric scaling rules. The optimal partitioning theory (OPT) predicts that plants allocate more biomass to the organ capturing the most limiting resource. • Whole-plant harvests of mature and juvenile tropical deciduous trees, evergreen trees, and lianas and model simulations were used to address the following knowledge gaps: (1) Do mature lianas comply with the APT scaling laws or do they invest less biomass in stems compared to trees? (2) Do juveniles follow the same allocation patterns as mature individuals? (3) Is either leaf phenology or life form a predictor of rooting depth? • It was found that: (1) mature lianas followed the same allometric scaling laws as trees; (2) juveniles and mature individuals do not follow the same allocation patterns; and (3) mature lianas had shallowest coarse roots and evergreen trees had the deepest. • It was demonstrated that: (1) mature lianas invested proportionally similar biomass to stems as trees and not less, as expected; (2) lianas were not deeper-rooted than trees as had been previously proposed; and (3) evergreen trees had the deepest roots, which is necessary to maintain canopy during simulated dry seasons.

• The optimal partitioning theory predicts that plants of a given species acclimate to different environments by allocating a larger proportion of biomass to the organs acquiring the most limiting resource. Are similar patterns found across species adapted to environments with contrasting levels of abiotic stress? • We tested the optimal partitioning theory by analysing how fractional biomass allocation to leaves, stems and roots differed between woody species with different tolerances of shade and drought in plants of different age and size (seedlings to mature trees) using a global dataset including 604 species. • No overarching biomass allocation patterns at different tolerance values across species were found. Biomass allocation varied among functional types as a result of phenological (deciduous vs evergreen broad-leaved species) and broad phylogenetical (angiosperms vs gymnosperms) differences. Furthermore, the direction of biomass allocation responses between tolerant and intolerant species was often opposite to that predicted by the optimal partitioning theory. • We conclude that plant functional type is the major determinant of biomass allocation in woody species. We propose that interactions between plant functional type, ontogeny and species-specific stress tolerance adaptations allow woody species with different shade and drought tolerances to display multiple biomass partitioning strategies.

Elucidating the variation of allocation pattern of ecosystem net primary productivity (NPP) and its underlying mechanisms is critically important for understanding the changes of aboveground and belowground ecosystem functions. Under optimal partitioning theory, plants should allocate more NPP to the organ that acquires the most limiting resource, and this expectation has been widely used to explain and predict NPP allocation under changing precipitation. However, confirmatory evidence for this theory has mostly come from observed spatial variation in the relationship between precipitation and NPP allocation across ecosystems, rather than directly from the influences of changing precipitation on NPP allocation within systems. We performed a 6-yr five-level precipitation manipulation experiment in a semiarid steppe to test whether changes in NPP allocation can be explained by the optimal partitioning theory, and how water requirement of plant community is maintained if NPP allocation is unaltered. The 30 precipitation levels (5 levels × 6 yr) were divided into dry, nominal, and wet precipitation ranges, relative to historical precipitation variation over the past six decades. We found that NPP in both aboveground (ANPP) and belowground (BNPP) increased nonlinearly as precipitation increased, while the allocation of NPP to BNPP (f BNPP) showed a concave quadratic relationship with precipitation. The declined f BNPP as precipitation increased in the dry range supported the optimal partitioning theory. However, in the nominal range, NPP allocation was not influenced by the changed precipitation; instead, BNPP was distributed more in the surface soil horizon (0–10 cm) as precipitation increased, and conversely more in the deeper soil layers (10–30 cm) as precipitation decreased. This response in root foraging appears to be a strategy to satisfy plant water requirements and partially explains the stable NPP allocation patterns. Overall, our results suggest that plants can adjust their vertical BNPP distribution in response to drought stress, and that only under extreme drought does the optimal partitioning theory strictly apply, highlighting the context dependency of the adaption and growth of plants under changing precipitation.

Plants respond to resource stress by changing multiple aspects of their biomass allocation, morphology, physiology and architecture. To date, we lack an integrated view of the relative importance of these plastic responses in alleviating resource stress and of the consistency/variability of these responses among species. We subjected nine species (legumes, forbs and graminoids) to nitrogen and/or light shortages and measured 11 above-ground and below-ground trait adjustments critical in the alleviation of these stresses (plus several underlying traits). Nine traits out of 11 showed adjustments that improved plants’ potential capacity to acquire the limiting resource at a given time. Above ground, aspects of plasticity in allocation, morphology, physiology and architecture all appeared important in improving light capture, whereas below ground, plasticity in allocation and physiology were most critical to improving nitrogen acquisition. Six traits out of 11 showed substantial heterogeneity in species plasticity, with little structuration of these differences within trait covariation syndromes. Such comprehensive assessment of the complex nature of phenotypic responses of plants to multiple stress factors, and the comparison of plant responses across multiple species, makes a clear case for the high (but largely overlooked) diversity of potential plastic responses of plants, and for the need to explore the potential rules structuring them.

Locally, plant species richness supports many ecosystem functions. Yet, the mechanisms driving these often-positive biodiversity-ecosystem functioning relationships are not well understood. Spatial resource partitioning across vertical resource gradients is one of the main hypothesized causes for enhanced ecosystem functioning in more biodiverse grasslands. Spatial resource partitioning occurs if species differ in where they acquire resources and can happen both above- and belowground. However, studies investigating spatial resource partitioning in grasslands provide inconsistent evidence. We present the results of a meta-analysis of 21 data sets from experimental species-richness gradients in grasslands. We test the hypothesis that increasing spatial resource partitioning along vertical resource gradients enhances ecosystem functioning in diverse grassland plant communities above- and belowground. To test this hypothesis, we asked three questions. (1) Does species richness enhance biomass production or community resource uptake across sites? (2) Is there evidence of spatial resource partitioning as indicated by resource tracer uptake and biomass allocation above- and belowground? (3) Is evidence of spatial resource partitioning correlated with increased biomass production or community resource uptake? Although plant species richness enhanced community nitrogen and potassium uptake and biomass production above- and belowground, we found that plant communities did not meet our criteria for spatial resource partitioning, though they did invest in significantly more aboveground biomass in higher canopy layers in mixture relative to monoculture. Furthermore, the extent of spatial resource partitioning across studies was not positively correlated with either biomass production or community resource uptake. Our results suggest that spatial resource partitioning across vertical resource gradients alone does not offer a general explanation for enhanced ecosystem functioning in more diverse temperate grasslands.

• Biomass and area ratios between leaves, stems and roots regulate many physiological and ecological processes. The Huber value Hv (sapwood area/leaf area ratio) is central to plant water balance and drought responses. However, its coordination with key plant functional traits is poorly understood, and prevents developing trait-based prediction models. • Based on theoretical arguments, we hypothesise that global patterns in Hv of terminal woody branches can be predicted from variables related to plant trait spectra, that is plant hydraulics and size and leaf economics. • Using a global compilation of 1135 species-averaged Hv , we show that Hv varies over three orders of magnitude. Higher Hv are seen in short small-leaved low-specific leaf area (SLA) shrubs with low Ks in arid relative to tall large-leaved high-SLA trees with high Ks in moist environments. All traits depend on climate but climatic correlations are stronger for explanatory traits than Hv . Negative isometry is found between Hv and Ks , suggesting a compensation to maintain hydraulic supply to leaves across species. • This work identifies the major global drivers of branch sapwood/leaf area ratios. Our approach based on widely available traits facilitates the development of accurate models of above-ground biomass allocation and helps predict vegetation responses to drought.

CONTENTS: Summary 30 I. Allocation in perspective 31 II. Topics of this review 32 III. Methodology 32 IV. Environmental effects 33 V. Ontogeny 36 VI. Differences between species 40 VII. Physiology and molecular regulation 41 VIII. Ecological aspects 42 IX. Perspectives 45 Acknowledgements 45 References 45 Appendices A1–A4 49 SUMMARY: We quantified the biomass allocation patterns to leaves, stems and roots in vegetative plants, and how this is influenced by the growth environment, plant size, evolutionary history and competition. Dose–response curves of allocation were constructed by means of a meta‐analysis from a wide array of experimental data. They show that the fraction of whole‐plant mass represented by leaves (LMF) increases most strongly with nutrients and decreases most strongly with light. Correction for size‐induced allocation patterns diminishes the LMF‐response to light, but makes the effect of temperature on LMF more apparent. There is a clear phylogenetic effect on allocation, as eudicots invest relatively more than monocots in leaves, as do gymnosperms compared with woody angiosperms. Plants grown at high densities show a clear increase in the stem fraction. However, in most comparisons across species groups or environmental factors, the variation in LMF is smaller than the variation in one of the other components of the growth analysis equation: the leaf area : leaf mass ratio (SLA). In competitive situations, the stem mass fraction increases to a smaller extent than the specific stem length (stem length : stem mass). Thus, we conclude that plants generally are less able to adjust allocation than to alter organ morphology.

Kin recognition is an important mediator of interactions within individuals of a species. Despite increasing evidence of kin recognition in natural plant populations, relatively little is known about kin recognition in crop species where numerous cultivars have been generated by artificial selection. We identified rice (Oryza sativa) cultivars with the ability for kin recognition from two sets of indica-inbred and indica-hybrid lines at different levels of genetic relatedness. We then assessed this ability among kin and nonkin and tested potential mechanisms in a series of controlled experiments and field trails. Rice cultivars with the ability for kin recognition were capable of detecting the presence of kin and nonkin and responded to them by altering root behavior and biomass allocation, particularly for grain yield. Furthermore, we assessed the role of root exudates and found a root-secreted nitrogen-rich allantoin component to be responsible for kin recognition in rice lines. Kin recognition in rice lines mediated by root exudates occurs in a cultivar-dependent manner. Rice cultivars with the ability for kin recognition may increase grain yield in the presence of kin. Such an improvement of grain yield by kin recognition of cultivar mixtures offers many implications and applications in rice production.

In recent years, belowground plant ecology has experienced a booming interest. This has resulted in major advances towards a greater understanding of belowground plant and ecosystem functioning focused on fine roots, mycorrhizal associations and nutrient acquisition. Despite this, other important functions (e.g., on‐spot persistence, space occupancy, resprouting after biomass removal) exerted by different belowground plant organs (e.g., roots, rhizomes, bulbs) remain largely unexplored. Here, we propose a framework providing a comprehensive perspective on the entire set of belowground plant organs and functions. We suggest a compartment‐based approach. We identify two major belowground compartments, that is, acquisitive and nonacquisitive, associated with biomass allocation into these functions. Also, we recommend the nonacquisitive compartment to be divided into structural (e.g., functional roles carried out by rhizomes, such as sharing of resources, space occupancy) and nonstructural (e.g., functional roles exerted by carbohydrates reserve affecting resprouting ability, protection against climate adversity) subcompartments. We discuss methodological challenges—and their possible solutions—posed by changes in biomass allocation across growth forms and ontogenetic stages, and in relation to biomass partitioning and turnover. We urge the implementation of methods and approaches considering all the belowground plant compartments. This way, we would make sure that key, yet less‐studied functions would be incorporated into the belowground plant ecology research agenda. The framework has potential to advance the understanding of belowground plant and ecosystem functioning by considering relations and trade‐offs between different plant functions and organs. At last, we identify four major areas where using the proposed compartment‐based approach would be particularly important, namely (a) biomass scaling, (b) clonality‐resource acquisition relations, (c) linkages between resprouting and changing environmental conditions and (d) carbon sequestration. A plain language summary is available for this article. Plain Language Summary Foreign Language Funkční ekologie podzemních částí rostlinSummary in Czech V posledních letech zažívá ekologie podzemních částí rostlin velký zájem výzkumníků po celém světě. Tento zájem přispěl k lepšímu porozumění funkce podzemních částí rostlin, zejména jemných kořenů a mykorhizy, které hrají významnou roli při získávání vody a živin. Jiné důležité funkce rostlin, jako je přežívání na daném místě, obsazování prostoru, nebo schopnost regenerace po poškození těla, zprostředkované například zásobními kořeny a oddenky, však zůstávají opomíjeny. S cílem napravit tuto situaci, navrhujeme integrovaný přístup, který umožní komplexnější pohled na celou řadu podzemních rostlinných orgánů a jejich funkcí. Na příkladech z literatury ukazujeme, jak zaměření pouze na jemné kořeny může omezit naši schopnost poznat ekologii rostlin. Navrhujeme přístup založený na rozlišení základních funkčních specializací podzemních orgánů. Identifikujeme dva hlavní funkční podzemní kompartmenty, za prvé akviziční, tj. podílející se na získávání vody a živin, a za druhé neakviziční, tj. podílející se na propojování různých částí rostliny, na klonálním růstu a na regeneraci po narušení. Diskutujeme metodologické problémy spojené s implementací tohoto přístupu a o jejich možných řešeních. Přestavujeme rozdíly v investicích do těchto podzemních kompartmentů u různých růstových forem a během života rostliny, stejně tak problémy související se stanovením biomasy a jejím obratem. Závěrem vyzýváme výzkumníky, aby při studium ekologie aplikovali metody a přístupy, které berou v úvahu všechny podzemní orgány rostlin. Pouze tímto způsobem zajistíme, aby méně studované, avšak zcela klíčové funkce podzemních orgánů rostlin, byly začleněny do výzkumného plánu funkčních ekologů. Příkladem může být jejich využití pro lepší odhad sekvestrace uhlíku v podzemních orgánech rostlin, což je důležité pro tvorbu celosvětových geochemických modelů.

1. Correlations among plant traits often reflect important trade-offs or allometric relationships in biological functions like carbon gain, support, water uptake, and reproduction that are associated with different plant organs. Whether trait correlations can be aggregated to \"spectra\" or \"leading dimensions,\" whether these dimensions are consistent across plant organs, spatial scale, and growth forms are still open questions. 2. To illustrate the current state of knowledge, we constructed a network of published trait correlations associated with the \"leaf economics spectrum,\" \"biomass allocation dimension,\" \"seed dimension,\" and carbon and nitrogen concentrations. This literature-based network was compared to a network based on a dataset of 23 traits from 2,530 individuals of 126 plant species from 381 plots in Northwest Europe. 3. The observed network comprised more significant correlations than the literature-based network. Network centrality measures showed that size traits such as the mass of leaf, stem, below-ground, and reproductive tissues and plant height were the most central traits in the network, confirming the importance of allometric relationships in herbaceous plants. Stem mass and stem-specific length were \"hub\" traits correlated with most traits. Environmental selection of hub traits may affect the whole phenotype. In contrast to the literature-based network, SLA and leaf N were of minor importance. Based on cluster analysis and subsequent PCAs of the resulting trait clusters, we found a \"size\" module, a \"seed\" module, two modules representing and N concentrations in plant organs, and a \"partitioning\" module representing organ mass fractions. A module representing the plant economics spectrum did not emerge. 4. Synthesis. Although we found support for several trait dimensions, the observed trait network deviated significantly from current knowledge, suggesting that previous studies have overlooked trait coordination at the whole-plant level. Furthermore, network analysis suggests that stem traits have a stronger regulatory role in herbaceous plants than leaf traits.