the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Mar 2024
Leaf habit and nutrient availability drive leaf nutrient resorption globally
Abstract. Nutrient resorption from senescing leaves can significantly affect ecosystem nutrient cycling, making it an essential process to better understand long-term plant productivity under environmental change that affects the balance between nutrient availability and demand. Although it is known that nutrient resorption rates vary strongly between different species and across environmental gradients, the underlying driving factors are insufficiently quantified. Here, we present an analysis of globally distributed observations of leaf nutrient resorption to investigate the factors driving resorption efficiencies for nitrogen (NRE) and phosphorus (PRE). Our results show that leaf structure and habit, together with indicators of nutrient availability, are the two most important factors driving spatial variation in NRE. Overall, we found higher NRE in deciduous plants (65.2 % ± 12.4 % , n=400) than in evergreen plants (57.9 % ± 11.4 %, n=551) , likely associated with a higher share of metabolic N in leaves of deciduous plants. Tropical regions show the lowest resorption for N (NRE: 52.4 % ± 12.1 % ) and tundra ecosystems in polar regions show the highest (NRE: 69.6 % ± 12.8 %), while the minimum PRE is in temperate regions (57.8 % ± 13.6 %) increasing to boreal regions (67.3 % ± 13.6 %). Soil clay content, N and P atmospheric deposition – a globally available proxy for soil fertility – and MAP played an important role in this pattern, where we found higher NRE and PRE in high latitudes. The statistical relationships developed in this analysis indicate an important role of leaf habit and type for nutrient cycling and guide improved representations of plant-internal nutrient re-cycling and nutrient conservation strategies in vegetation models.
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RC1: 'Comment on egusphere-2024-687', Anonymous Referee #1, 10 Apr 2024
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The authors present impressive insights into the major drivers of nutrient resorption at a global scale. This study identifies leaf habit and leaf type as major biotic drivers of nutrient resorption, alongside climate and nutrient-related factors as major abiotic drivers. This finding addresses discrepancies observed in previous studies, offering valuable clarity to the field. As a result, this study deserves broader recognition and could serve as a benchmark for future research. The manuscript is clear, making it easy to read. Therefore, I recommend acceptance of the manuscript, with a few questions that need to be addressed.
Firstly, considering the authors' findings that different functional groups exhibit varying nutrient resorption efficiencies, I wonder whether these rates are evolutionarily conservative. If species within the same family share similar resorption rates, it could provide valuable insights into functional consequences of climate change and potential shifts in plant communities.
The authors selected the best combination of variables based on AIC and BIC values, leading to the exclusion of SLA from the models presented in Table 3. However, from an ecological perspective, understanding the role of SLA while controlling for other environmental factors would be beneficial. Given the authors' observation that "thicker, longer-lived leaves have lower resorption efficiencies," it would be informative to include a model demonstrating the relationship between SLA and nutrient resorption efficiency (NRE or PRE), providing further insight into the mechanisms driving spatial variation in nutrient resorption.
The global analysis presented in this study offers valuable insights. However, there is a need to balance the sample size across climatic zones. It's possible that the dataset over-represents dry regions, which could skew the results. Therefore, I suggest the authors consider a down-sampled dataset to ensure a more balanced representation of different climatic zones. I find it interesting that leaf type significantly influences PRE, and I believe this could represent a facilitative strategy for needle-leaved plants to support cell structures in nutrient-poor habitats. However, upon closer examination of the sample sizes, I am concerned that this result may be biased by the unbalanced distribution of samples across different biomes.
Some minor comments:
L.185-187: Like what I mentioned above, temperate biomes are over-represented. I wonder if this can influence your analysis result.
L.237: you may miss a standard deviation here for NRE.
297-310: It would be helpful to see the explanatory powers of the dredge models and separated explanatory powers by biotic and abiotic groups of factors.
Citation: https://doi.org/10.5194/egusphere-2024-687-RC1 -
RC2: 'Comment on egusphere-2024-687', Helena Vallicrosa, 12 Apr 2024
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In this study, Sophia et al. explore the N and P resorption efficiency of woody plants to find global patterns and their main drivers. They conclude that nutrient availability and leaf habit are its main drivers, with a substantial effect of climatic factors.
I found the scope of the study very relevant, and the paper to be comprehensive and beautifully written. Nonetheless, I missed further attention to some aspects that I further develop:
- I appreciate the authors including a discussion about the quality of the data used for the paper. I indeed acknowledge the difficulty of obtaining paired good-quality data on the explored variables. Nonetheless, I believe that there are some further concerns about the data quality or treatment that haven’t been reported or discussed:
- The percentage of interpolated or gap-filled data included in the analysis should be reported (Line 174-180). Currently, the reader does not have a way to know how much real field data is in there.
- The time aspect of the data collection should be clarified. Have the green leaf and litter samples been taken at the same time? Did you consider a one-year gap between green leaf and litter? (Since in deciduous trees litter corresponds to the previous season’s green leaves).
- I assume there is no way to certify that the leaf and litter samples are coming from the same individual and you might have been comparing green leaves and litter from different individuals (even though they are the same species). How big do you think this intraspecific variability is?
- Nutrient reabsorption is also used for nutrient limitation assessment (i.e. Du et al., 2020 cited by authors, or Li et al., 2010…), a concept that authors here refer to as “plant nutrient demand”, I believe (line 84-85). The higher the nutrient limitation, the higher the nutrient reabsorption. Therefore, it would be expected that N deposition would be inversely related to NRE, which is what happens with P deposition and PRE. Nonetheless, and according to your reported results, NRE and N deposition are positively correlated, meaning that more N deposition is related to an increase in NRE (Table 3). At the same time, N deposition is considered the most important variable for NRE (Figure 5a). I believe it is a very counterintuitive and interesting result but I couldn’t find further discussion about it in section 4.3. Could you please dig further in?
- The authors have acknowledged that the data availability to perform this study could be more representative if more data were available. The authors also acknowledged that the results for the needle leave category are mostly based on the Pinaceae family. There is evidence that foliar N and P are strongly influenced by species identity (i.e. Sardans et al., 2021). Perhaps, including the species identity or the phylogenetic distance in your models could improve the reliability of your results. It could be worth exploring.
- The title does not fully convince me; I don’t think it fully represents your conclusions and therefore results. For example, climate is not mentioned even though you conclude to have a significant role (Line 567).
MINOR COMMENTS
Line 52: This sentence sounds weird. Maybe changing implies by imply?
Line 64: How is “soil fertility” defined? Since it is an important concept for the paper I believe further definition is required.
Line 153: Why 2010? Don’t you have the year when the data was collected? There are yearly N deposition maps where you could extract the information from. The temporality in Ndep is relevant since it has changed substantially over time, especially in the areas where most of the data is coming from (Ackermann et al., 2019). What do you mean when saying “considering that the fields are relatively smooth”?
Line 343-348: Does this correlate with studies accounting or not for the MLCF?
Line 437-438: There might be a mistake on “low MAP leads to soil moisture”. It should be “low MAP leads to low soil moisture”, right?
General rambling questions:
Can plants make a difference between elements when reabsorbing? For example: If they would be very N limited but P abundant, could they actually “decide” what element to reabsorb?
Do the reabsorption % align with N:P ratios in fresh leaves?
Ackerman, D., Millet, D. B., & Chen, X. (2019). Global estimates of inorganic nitrogen deposition across four decades. Global Biogeochemical Cycles, 33, 100–107. https://doi.org/10.1029/2018GB005990
XuefengLiX. Li, XingboZhengX. Zheng, ShijieHanS. Han, JunqiangZhengJ. Zheng, and TonghuaLiT. Li. 2010. Effects of nitrogen additions on nitrogen resorption and use efficiencies and foliar litterfall of six tree species in a mixed birch and poplar forest, northeastern China. Canadian Journal of Forest Research. 40(11): 2256-2261.
Sardans, J., Vallicrosa, H., Zuccarini, P. et al. Empirical support for the biogeochemical niche hypothesis in forest trees. Nat Ecol Evol 5, 184–194 (2021). https://doi.org/10.1038/s41559-020-01348-1
Helena Vallicrosa
Citation: https://doi.org/10.5194/egusphere-2024-687-RC2 - I appreciate the authors including a discussion about the quality of the data used for the paper. I indeed acknowledge the difficulty of obtaining paired good-quality data on the explored variables. Nonetheless, I believe that there are some further concerns about the data quality or treatment that haven’t been reported or discussed:
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