Nitrogen uptake strategies of mature conifers in Northeastern China, illustrated by the 15N natural abundance method

Background Conifers partition different N forms from soil, including ammonium, nitrate, and dissolved organic N (DON), to sustain plant growth. Previous studies focused on inorganic N sources and specific amino acid forms using 15N labelling, but knowledge of the contribution of DON to mature conifers’ N uptake is still scarce. Here, we quantified the contribution of different N forms (DON vs. NH4+ vs. NO3−) to total N uptake, based on 15N natural abundance of plant and soil available N, in four mature conifers (Pinus koraiensis, Pinus sylvestris, Picea koraiensis, and Larix olgensis). Results DON contributed 31%, 29%, 28%, and 24% to total N uptake by Larix olgensis, Picea koraiensis, Pinus koraiensis, and Pinus sylvestris, respectively, whereas nitrate contributed 42 to 52% and ammonium contributed 19 to 29% of total N uptake for these four coniferous species. Conclusions Our results suggested that all four conifers could take up a relatively large proportion of nitrate, while DON was also an important N source for the four conifers. Given that DON was the dominant N form in study soil, such uptake pattern of conifers could be an adaptive strategy for plants to compete for the limited available N sources from soil so as to promote conifer growth and maintain species coexistence.

Nutrient Dynamics Assessment of Coarse Wood Debris Subjected to Successional Decay Levels of Three Forests Types in Northeast, China

Coarse wood debris (CWD) plays a critical role in forest productivity, nutrient cycling, decomposition, and carbon sequestration, and shapes the carbon pool in the forest ecosystem. However, the elemental composition of CWD varies among different forest types and decay classes for the same dominant tree species (Pinus koraiensis, PK). We compared CWD elemental composition across different forest types (Picea koraiensis-Abies nephrolepis-Pinus koraiensis forest (PAPF), Betula costata-Pinus koraiensis forest (BPF), Tilia amurensis-Pinus koraiensis forest (TPF)), considering four classes of wood decay. Results showed that N, P, Mg, Mn, Na, Zn, S, Al, and Fe concentrations almost totally increased with decay level for all three forest types, except for K in all three forest types and B in Picea koraiensis-Abies nephrolepis-Pinus koraiensis forest (PAPF). Similarly, maximum concentrations of N, P, B, Mg, K, C, Zn, and Mn of CWD were observed in Betula costata-Pinus koraiensis forest (BPF) under varying decay classes, but their maximum concentrations of Fe and S were found in Picea koraiensis-Abies nephrolepis-Pinus koraiensis forest (PAPF) and Tilia amurensis-Pinus koraiensis forest(TPF), respectively. Only C content did not significantly differ in decay classes across all three forest types. The C:N ratio decreased significantly with increasing decay levels across all forest types. The decay rates were significantly related to N concentration and C:N ratio in decay classes across all forest types. These results suggest that C and N concentration are the key factors affecting its decomposition. The variation in nutrient concentrations observed here underscores the complexity of nutrients stored in wood debris in forested ecosystems.

Prediction of Needle Chlorophyll Model with Different Leaf Ages Based on BP Neural Network and PLSR

BackgroundTo explore the changes of chlorophyll content in needles of different leaf ages of Picea koraiensis Nakai of different specifications, the study compared the prediction accuracy changes of chlorophyll in needles of Picea koraiensis Nakai by two modeling methods: the BP neural network and partial least squares regression (PLSR) methods. The effects of different spectral pre-processing and characteristic band selection methods on the performance accuracy of the model were tested, and the optimal combination model was selected to predict forest growth status and community structure productivity through the physiological and biochemical characteristics of needles at different leaf ages. Results1) the spectral pre-processing method could avoid systematic errors and eliminate background values; 2) the accuracy of the needle chlorophyll fitting model with different leaf ages was much higher than that of mixed needle chlorophyll model, verifying that needle chlorophyll with different leaf ages could better estimate the annual growth and examine the growth status of Picea koraiensis Nakai; 3) the accuracy of the BP neural network model was significantly higher than that of the PLSR model, with its R 2 above 0.95, and the validation set’s R 2 above 0.86; and 4) the fitting accuracy of different leaf age needle chlorophyll models of the spectral pre-processing model, variable selection model, PLSR model and BP neural network: triennial needles > annual and biennial needles. ConclusionsThe BP neural network method was more accurate than the PLSR method in predicting pigment content model. In the process of model fitting, it was found that the pigment model fitted by fine classification of needles improves the accuracy of the model, which provides the basis and theoretical support for the establishment of the model by combining remote sensing technology with stoichiometry methods in the future.

Phytohormones Regulate Both “Fish Scale” Galls and Cones on Picea koraiensis

The larch adelgid Adelges laricis laricis Vallot is a specialist insect parasite of Picea koraiensis (Korean spruce) and forms fish scale-like galls that damage the growth of the host plants. Our investigation reveals that both these galls and the fruits (cones) of P. koraiensis display lower concentrations of phytosynthetic pigments and accumulate anthocyanin cyanidin-3-O-glucoside and soluble sugars in the mature stages. Interestingly, high concentrations of 6-benzylaminopurine (BAP) both in the cauline gall tissues and in the larch adelgids themselves (4064.61 ± 167.83 and 3655.42 ± 210.29 ng/g FW, respectively), suggested that this vital phytohormone may be synthesized by the insects to control the development of gall tissues. These results indicate that the galls and cones are sink organs, and the development of gall tissues is possibly regulated by phytohormones in a way similar to that of the growth of cones. The concentrations of phytohormones related to growth [indole-3-acetic acid (IAA), cytokinins (CTK), and gibberellins (GAs)] and defense [salicylic acid (SA)], as well as SA-related phenolics [benzoic acid (BA) and p-hydroxybenzoic acid (pHBA)] in gall tissues were positively correlated with those in cones during the development stage. The levels of 1-aminocyclopropane-1-carboxylic acid (ACC) in the developmental stage of the cones correlates negatively with their concentrations in the gall tissues (R = −0.92, p < 0.001), suggesting that downregulation of ACC might be the reason why galls are not abscised after a year. Our results provide a new perspective on the potential mechanism of the development of cauline galls on P. koraiensis, which are regulated by phytohormones.

Короїди хвойних порід Ботанічного саду Харківського національного університету ім. В. М. Каразіна

На території Ботанічного саду Харківського національного університету (ХНУ) ім. В. М. Каразіна на хвойних породах визначено 4 види короїдів: короїда-типографа (Ips typographus L.), гравера звичайного (Pityogenes chalcographus L.), соснового короїда-крихітку (Crypturgus cinereus Herb.) та тайгового короїда-крихітку (C. subcribrosus Eg.). Відзначено, що з роду Abies лише п’ять видів не мали ознак заселення, а саме: A. balsamia, A. cephalonica, А. concolor, A. grandis, А. violacea. Picea koraiensis та P. alba не були заселені короїдами, але на стовбурі помічено спроби заселення. Встановлено, що форму P. obovata «Glauca» заселяли всі визначені види короїдів. Найбільш поширеним на ялині серед інших видів короїдів виявився Ips typographus. Серед 198 обстежених дерев визначено: живих із відсутністю ознак заселення короїдами – 27,3 %, зі спробами заселення – 9,1 %, заселених короїдами – 63,6 %.