تاثیر پوسته‌های زیستی در افزایش اسیدهای آلی خاک و آهن قابل دسترس گیاه در خاک‌های بیابان سجزی

پوسته‌های زیستی خاک عملکرد ویژه‌ای در چرخۀ جهانی کربن و افزایش مادۀ آلی خاک به‌خصوص در مناطق خشک و نیمه‌خشک دارند. کربن آلی خاک که آمیخته‌ای از بخش‌های گوناگون از جمله اسیدهای آلی می‌باشد، از شناسه‌های مهم برای بررسی کیفیت خاک است. اسیدهای آلی، قابلیت انحلال عناصر غذایی کم محلول از جمله آهن خاک را افزایش می‌دهند. در این پژوهش، اثر پوسته‌های زیستی در افزایش اسیدهای آلی خاک و و مشارکت آن‌ها در واجذب آهن بررسی شده است. بدین منظور پس از تهیۀ نقشۀ پراکنش پوسته‌های زیستی در دشت سجزی از خاک زیر پوشش پوسته‌های زیستی با غالبیت گلسنگ نمونه‌برداری شد. خصوصیات فیزیکوشیمیایی خاک شامل اسیدیته، هدایت الکتریکی، مقادیر مادۀ آلی، آهن و بافت خاک اندازه‌گیری شدند. ضریب همبستگی پیرسون بین درصد مادۀ آلی و پوشش پوسته‌های زیستی 653/0 محاسبه شد که نشان‌دهندۀ اهمیت پوسته‌های زیستی در افزایش کربن آلی خاک بود. همچنین نتایج آزمون tstudent نشان داد که مقادیر آهن قابل جذب در خاک زیر پوشش پوسته‌های زیستی و بدون پوسته‌های زیستی اختلاف معنی‌دار دارند. با رسته‌بندی پارامتر‌های به روش pca معلوم شد که در دشت سجزی با اطمینان 51/67%، شوری خاک و در سطح 73/21%، بافت خاک و آهک جزء مهم‌ترین عوامل محدود‌کنندۀ استقرار پوسته‌های زیستی هستند. برای تشخیص وجود عامل اسید آلی در خاک آزمون مادون قرمز فوریه انجام یافت و طیف‌های ftir برای نمونه‌های خاک به دست آمد. اسید سیتریک و اسید اگزالیک به‌ترتیب در طول موج‌های 1400 تا 1600 (cm1) و 1700 تا 1800 (cm1) قرائت شدند. بنابراین پوسته‌های زیستی از طریق افزایش اسیدهای آلی که بخشی از کل مادۀ آلی خاک را تشکیل می‌دهند، در افزایش آهن قابل جذب خاک نقش موثری دارند.

Investigating the Effect of Biocrusts on increasing the soil's organic acids and absorbable iron in desert soils

Extended AbstractIntroduction: The soilchr('39')s biological crusts increase soilchr('39')s organic matter, especially in arid and semiarid regions, performing a special function in the global carbon cycle. Organic soil carbon, which is a mixture of various components, including organic acids, is an important indicator of soil quality. Organic acids increase the solubility of lowsoluble nutrients, including soil iron. Therefore, this study attempted to investigate the effect of biological shells in increasing soil organic acids and their participation in iron uptake. Materials and Methods: The map of biological soil crustschr('39') distribution in the Sejzi plain was prepared, and soil was sampled under cover of biological soil crusts from lichendominated areas. Then, soilchr('39')s physicochemical properties, including pH, EC, Fe, OC%, CaCO3%, and soil texture, were measured. Next, the Pearson correlation coefficient was calculated to determine the relationship between soil parameters and biological soil crusts. The values of the soilchr('39')s physicochemical parameters were classified into two classes (soils covered by biocrust and nonbiocrust) via PCA (Principal Component Analysis) using Matlab 2013b software. Then, loading charts for the first, second, and third components were calculated at the confidence level of 67.51%, 21.73%, and 6.71%, respectively. FourierTransform Infrared spectroscopy was performed, and FTIR spectra were obtained for all collected soil samples to identify the existence of an organic acid agent in the soil.Results: In the study area, 32 specimens of terrestrial lichens were collected from the Sejzi desert, most of which had been classified as cyanolichens whose photobiont part was cyanobacteria.The Pearson correlation coefficient between the percentage of organic matter and the coating of biological soil crusts was reported to be 0.653, indicating the significance of biological soil crusts in increasing soil organic carbon. Also, the results of the tStudent test showed that the amounts of absorbable iron in biocrustcovered and biocrustfree soils were significantly different.The classification of the relevant parameters via the PCA method revealed that in the Sejzi plain, soil salinity with 67.51% confidence, and at 21.73% level, soil texture and lime percentage were among the most important limiting factors in the establishment of biological soil crusts.Based on FTIR curves, Citric acid and oxalic acid were read from 1400 to 1600 (cm1) and 1700 to 1800 (cm1), respectively.Discussion and conclusion: Deserts, arid, and semiarid ecosystems contain very small amounts of organic matter, and, thus, they are exposed to the destructive effects of physical and chemical agents. Therefore, biocrusts, which play a very influential role in increasing the soilchr('39')s organic compounds, improve the properties of desertified soils and enhance the desertchr('39')s health. Moreover, secreting organic acids that form part of the whole soilchr('39')s organic matter, biological soil crusts act like plant roots and facilitate chemical reactions in arid and semiarid soils that are considered poor in terms of fertility. According to the studychr('39')s findings, calcium carbonate, which increases soil alkalinity and affects the establishment of biological soil crusts, was found to be a limiting factor in carbon sequestration in the Sejzi plain. In other words, with an increase in calcium carbonate, the carbon sequestration and the amount of soilchr('39')s organic carbon decreased.On the other hand, increased pH in the soil reduces the efficiency of organic acids such as citrate and oxalate, and as a result, the plantschr('39') absorption of the soilchr('39')s micronutrients, including the iron, was reduced, and the growth of aerial parts and roots of the plant was disrupted.Furthermore, it was found that the probability of the formation of the lichendominated biological crust is 21.73% in sandy and silty soils, which contain more sand and silt than the clay soils. Also, in the Sejzi plain, fewer biocrusts are established in calcareous soils. Moreover, in deserts, biocrusts increase organic carbon and thus perform different functions compared to other regions. However, they do not increase aggregate soil stability by increasing calcium carbonate. It should be noted that most of the Sejzi desertchr('39')s biocrusts produce organic matter and increase soilchr('39')s organic carbon, and a few of them are of calcium carbonateproducing types. Finally, it could be argued that biological soil crusts significantly increased iron absorption, which is considered as one of the most important micronutrients in the soil, by increasing the organic matter, which is among the categories found in the soilchr('39')s organic matter. An increase in iron absorption was especially significant in the Sejzi plainchr('39')s soils with high alkalinity (pH 7.5), limiting micronutrients dissolution and subsequently disrupting the establishment of vegetation.