The mechanisms governing tree drought mortality and recovery remain a subject of inquiry and active debate given their role in the terrestrial carbon cycle and their concomitant impact on climate ...change. Counter‐intuitively, many trees do not die during the drought itself. Indeed, observations globally have documented that trees often grow for several years after drought before mortality. A combination of meta‐analysis and tree physiological models demonstrate that optimal carbon allocation after drought explains observed patterns of delayed tree mortality and provides a predictive recovery framework. Specifically, post‐drought, trees attempt to repair water transport tissue and achieve positive carbon balance through regrowing drought‐damaged xylem. Furthermore, the number of years of xylem regrowth required to recover function increases with tree size, explaining why drought mortality increases with size. These results indicate that tree resilience to drought‐kill may increase in the future, provided that CO2 fertilisation facilitates more rapid xylem regrowth.
The current generation of dynamic global vegetation models (DGVMs) lacks a mechanistic representation of vegetation responses to soil drought, impairing their ability to accurately predict Earth ...system responses to future climate scenarios and climatic anomalies, such as El Niño events. We propose a simple numerical approach to model plant responses to drought coupling stomatal optimality theory and plant hydraulics that can be used in dynamic global vegetation models (DGVMs). The model is validated against stand-scale forest transpiration (E) observations from a long-term soil drought experiment and used to predict the response of three Amazonian forest sites to climatic anomalies during the twentieth century. We show that our stomatal optimization model produces realistic stomatal responses to environmental conditions and can accurately simulate how tropical forest E responds to seasonal, and even long-term soil drought. Our model predicts a stronger cumulative effect of climatic anomalies in Amazon forest sites exposed to soil drought during El Niño years than can be captured by alternative empirical drought representation schemes. The contrasting responses between our model and empirical drought factors highlight the utility of hydraulically-based stomatal optimization models to represent vegetation responses to drought and climatic anomalies in DGVMs.
This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.
The maximum Rubisco carboxylation rate normalized to 25 °C (Vcmax25) is a key parameter in terrestrial biosphere models for simulating carbon cycling. Recently, global distributions of Vcmax25 have ...been derived through various methods and different data, including field measurements, ecological optimality theory (EOT), leaf chlorophyll content (LCC), and solar-induced chlorophyll fluorescence (SIF). However, direct validation poses challenges due to high uncertainty arising from limited ground-based observations. This study conducted an indirect evaluation of four Vcmax25 datasets by assessing the accuracy of gross primary productivity (GPP) simulated using the Biosphere-atmosphere Exchange Process Simulator (BEPS) at both site and global scales. Results indicate that, compared to utilizing Vcmax25 fixed by plant functional types (PFT) derived from field measurements, incorporating Vcmax25 derived from SIF and LCC (SIF + LCC), or solely LCC, into BEPS significantly reduces simulated errors in the annual total GPP, with a 23.2 %–25.1 % decrease in the average absolute bias across 196 FLUXNET2015 sites. Daily GPP for evergreen needleleaf forests, deciduous broadleaf forests, shrublands, grasslands, and croplands shows a 7.8 %–27.6 % decrease in absolute bias, primarily attributed to reduced simulation errors during off-peak seasons of vegetation growth. Conversely, the annual total GPP error simulated using EOT-derived Vcmax25 increases slightly (2.2 %) compared to that simulated using PFT-fixed Vcmax25. This is primarily due to a significant overestimation in evergreen broadleaf forests and underestimation in croplands, despite slight increased accuracy for other PFTs. The global annual GPP simulated using Vcmax25 with seasonal variations (i.e., LCC Vcmax25 and SIF + LCC Vcmax25) yields a 4.3 %–7.3 % decrease compared to that simulated using PFT-fixed Vcmax25. Compared to FLUXCOM and GOSIF GPP products, the GPP simulated based on SIF + LCC Vcmax25 and LCC Vcmax25 demonstrates better consistency (R2 = 0.91–0.93, RMSE = 314.2–376.6 g C m−2 yr−1). This study underscores the importance of accurately characterizing the spatiotemporal variations in Vcmax25 for the accurate simulation of global vegetation productivity.
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•Comparing four datasets of maximum carboxylation rate normalized to 25 °C (Vcmax25).•Four Vcmax25 datasets reveal significant global spatial and temporal differences.•GPP modeled using leaf chlorophyll content and SIF Vcmax25 has the highest accuracy.•Ecological optimal Vcmax25 overestimates tropical GPP, underestimates cropland GPP.•GPP modeled using Vcmax25 with seasonal variations has lower global annual values.
Artykuł postuluje, iż kształt reprezentacji segmentów mowy w językach świata jest regulowany przez aktywność zasady *Hydra, która wskazuje jako nacechowane takie reprezentacje segmentalne, w których ...więcej niż jeden element pełni funkcję elementu nadrzędnego. W artykule wykazujemy, iż w językach takich jak francuski czy portugalski zasada *Hydra ma decydujący wpływ zarówno na kształt inwentarza samogłosek nosowych, jak i na wyniki pewnych procesów fonologicznych. Równocześnie zachowanie samogłosek nosowych w języku joruba wskazuje na nieabsolutną naturę zasady *Hydra. W języku polskim aktywność tej zasady jest niezbędna do zrozumienia zjawiska braku zmiękczenia spółgłosek tylnojęzykowych w kontekście samogłoski nosowej /ɛ/͂ oraz mechanizmów odpowiedzialnych za fakt, iż morfonologiczne zmiękczenia spółgłosek tylnojęzykowych, wargowych i zębowych mają miejsce w kontekście tych samych przyrostków słowotwórczych.
The paper proposes that the phonological make-up of segments is influenced by the activity of the constraint *Hydra, which penalizes the presence of more than one headed element per one phonological expression. *Hydra influences the shape of the inventories and the phonological behaviour of nasal vowels in languages such as French and Brazilian Portuguese. At the same time, the behaviour of nasal vowels in Yoruba shows that *Hydra a violable constraint. In Polish, the high ranking of *Hydra proves necessary to account for the absence of Surface Velar Palatalization before the front nasal vowel /ɛ/. It also allows us to formulate a unified account of the 1st Velar and Anterior Palatalization, which have very different structural descriptions but take place before the same set of derivational affixes.
A purely phonological account of reduplication based on the affixation of empty prosodic nodes predicts the attested typology of multiple reduplication. Languages that can combine more than one ...reduplication-triggering morpheme in a word differ in (1) whether all reduplicants surface faithfully, (2) whether they systematically avoid adjacent multiple reduplicants, or (3) whether one of the reduplicants is smaller than expected if another reduplicant is adjacent in multiple reduplication contexts. Morphological accounts of reduplication not only violate the modularity between phonology and morphology, they also fail to predict this attested typology.
Two conceptions of the linguistic system of bilinguals are in contention. The
approach supports what we call a
view, arguing that bilingualism and multilingualism, despite their importance as ...sociocultural concepts, have no correspondence in a dual or multiple linguistic system. In our view, the myriad lexical and structural features mastered by bilinguals occupy a cognitive terrain that is not fenced off into anything like the two areas suggested by the two socially named languages. But a strong critique of this view by Jeff MacSwan adopts the familiar position that, while allowing for some overlap, the competence of bilinguals involves language specific internal differentiation. According to this view, which we have called the
, bilinguals possess two separate linguistic systems whose boundaries coincide with those of the two named languages. Several interdisciplinary considerations point to the lack of initial plausibility of the dual correspondence theory. And the main argument offered by MacSwan in defense of the theory, namely restrictions on code switching, lacks descriptive adequacy and theoretical coherence. The dual correspondence theory has had pernicious effects in educational practices. A much healthier educational climate is created by teachers who adopt the unitary view sponsored by translanguaging.
This research aims to examine the Englyn meter in the poetry of Celtic language (Medieval Welsh) that requires the poetic texts to conform to an abstract prosodic template. This counting meter ...regulates the phonological constituency on the same metric level of the prosodic hierarchy rather than on the metrical hierarchy in verse (the line). In the main types of Englyn meters, Englyn milwr and Englyn penfyr, phonological units of each line are constrained with a certain number of syllables and rhyme with the final syllable of most lines. This research offers a markedness-based analysis that generates the well-formedness meter of Celtic language Welsh poetry. The Optimality Theoretical analysis derives the constraint on the phonological constituency over a certain metric level of the prosodic hierarchy (the line) with markedness constraints. Further coping constraints that are normally used for reduplication are needed to account for the rhyme of the final syllable in Englyn meter. The analysis offered supports the Development hypothesis, which is fundamental to generative metrics indicating that meter is evidently related to general language phonology. These results could help analyse other counting meters with restricted phonological constituency.
Support vector machines (SVM), as one of effective and popular classification tools, have been widely applied in various fields. However, they may incur prohibitive computational costs when solving ...large-scale classification problems. To address this problem, we construct a new fast SVM with a truncated squared hinge loss (dubbed as Lts-SVM). We begin by developing an optimality theory of the nonconvex and nonsmooth Lts-SVM, which makes it convenient for us to investigate the support vectors and working set of Lts-SVM. Based on this, we propose a new and effective global convergence algorithm to address the Lts-SVM. This method is found to enjoy a tremendously low computational complexity, which makes sufficiently decreasing the demand for extremely large-scale computation possible. Numerical comparisons with eight other solvers show that our proposed algorithm achieves excellent performance on large-scale classification problems with regard to shorter computational times, more desirable accuracy levels, fewer support vectors and more robust to outliers.
•The new SVM model. We construct a new SVM model, which is named as truncated squared hinge loss SVM model.•The new and efficient ADMM algorithm. We propose a new and effective alternating direction method of multipliers with working set for solving the truncated squared hinge loss SVM model.•High numerical performance. We compare our algorithm with eight other efficient solvers. Numerical experiments show that our algorithm shares excellent performance.
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