تأثير تيپ جامعه گياهي بر توزيع اندازه خاكدانه‌ها در حوضه گنبد (همدان)

The Effect of Plant Community Type on Soil Aggregate Size Distribution in Gonbad Watershed (Hamadan

مقدار و تركيب بيوشيميايي بقاياي گياهي وارد شده به خاك بر سرعت خاك­دانه‌سازي و پايداري خاك­دانه­ ها مؤثر اﺳﺖ. ﺑﻪﻣﻨﻈﻮر ﺑﺮرﺳﯽ ﺗﺄﺛﯿﺮ ﭘﻮﺷﺶﻫﺎي ﮔﯿﺎﻫﯽ ﻣﺨﺘﻠﻒ ﺑﺮ ﺗﻮزﯾﻊ اﻧﺪازه ﺧﺎكداﻧﻪﻫﺎ، ﭘﻨﺞ ﺗﯿﭗ ﮔﯿﺎﻫﯽ ﺷﺎﻣﻞ ﮔﻨﺪم دﯾﻢ، ﮔﻨﺪﻣﯿﺎن، ﮔﻮن-ﺑﺮوﻣﻮس، ﮔﻮن-ﺟﺎرو و ﮔﻮن-درﻣﻨﻪ در ﺷﺮاﯾﻂ ﻣﺤﯿﻄﯽ ﻣﺸﺎﺑﻪ از ﻧﻈﺮ ﻣﻮاد ﻣﺎدري و ﺟﻬﺖ ﺷﯿﺐ در ﺣﻮﺿﻪ آﺑﺨﯿﺰ ﮔﻨﺒﺪ واﻗﻊ در ﻫﻤﺪان، ﻣﻄﺎﻟﻌﻪ ﺷﺪ. ﮐﺮﺑﻦ آﻟﯽ ﮐﻞ، ﮐﺮﺑﻮﻫﯿﺪرات، ﻣﯿﺎﻧﮕﯿﻦ وزﻧﯽ ﻗﻄﺮ ﺧﺎكداﻧﻪﻫﺎ، ﺗﻮزﯾﻊ اﻧﺪازه ﺧﺎكداﻧﻪ و ﮐﺮﺑﻦ ﺧﺎكداﻧﻪاي در ﺧﺎك ﺳﻄﺤﯽ )0-15 ﺳﺎﻧﺘﯽﻣﺘﺮ( اﻧﺪازهﮔﯿﺮي ﺷﺪ. ﮐﺮﺑﻦ آﻟﯽ، ﮐﺮﺑﻮﻫﯿﺪرات، ﻣﯿﺎﻧﮕﯿﻦ وزﻧﯽ ﻗﻄﺮ ﺧﺎكداﻧﻪﻫﺎ و ﮐﺮﺑﻦ آﻟﯽ ﺧﺎكداﻧﻪاي )ﻣﻮﺟﻮد در ﻫﻤﻪ ﺑﺨﺶﻫﺎي اﻧﺪازه ﺧﺎكداﻧﻪاي( در ﺧﺎكﻫﺎي ﺗﺤﺖ ﭘﻮﺷﺶ ﮔﻮن-ﺑﺮوﻣﻮس و ﮔﻮن-درﻣﻨﻪ ﺑﻪﻃﻮر ﻣﻌﻨﯽداري ﺑﯿﺸﺘﺮ از ﺧﺎك ﺗﺤﺖ ﺗﯿﭗﻫﺎي دﯾﮕﺮ ﺑﻮد و ﮐﻤﺘﺮﯾﻦ ﻣﻘﺪار اﯾﻦ ﺷﺎﺧﺺﻫﺎ در ﺧﺎكﻫﺎي داراي ﭘﻮﺷﺶ ﮔﻨﺪﻣﯿﺎن و ﮔﻨﺪم دﯾﻢ ﻣﺸﺎﻫﺪه ﺷﺪ. ﺑﯿﺸﺘﺮﯾﻦ درﺻﺪ ﺧﺎكداﻧﻪﻫﺎي ﺑﺰرﮔﺘﺮ از 2 ﻣﯿﻠﯽﻣﺘﺮ و ﮐﻤﺘﺮﯾﻦ درﺻﺪ ﺧﺎكداﻧﻪﻫﺎي ﮐﻮﭼﮑﺘﺮ از 0/5 ﻣﯿﻠﯽﻣﺘﺮ در ﺧﺎك ﺗﯿﭗ ﮔﻮن- ﺑﺮوﻣﻮس ﻣﺸﺎﻫﺪه ﺷﺪ. در ﺗﯿﭗﻫﺎي ﮔﻮن-ﺑﺮوﻣﻮس و ﮔﻮن-درﻣﻨﻪ ﻣﻘﺪار ﺗﺎج ﭘﻮﺷﺶ ﮔﯿﺎﻫﯽ، ﺗﻮﻟﯿﺪ ﺳﺎﻻﻧﻪ، ﺗﻨﻮع ﮔﻮﻧﻪاي و ﻻﺷﺒﺮگ ﺑﯿﺸﺘﺮ از دﯾﮕﺮ ﺗﯿﭗﻫﺎ اﻧﺪازهﮔﯿﺮي ﺷﺪ. ﺗﯿﭗ ﮔﻨﺪم دﯾﻢ ﺑﻪﻋﻠﺖ ﻋﻤﻠﯿﺎت ﺧﺎكورزي و ﺗﯿﭗﻫﺎي ﮔﻮن-ﺟﺎرو و ﮔﻨﺪﻣﯽ ﺑﻪ ﻋﻠﺖ ﭘﻮﺷﺶ ﮔﯿﺎﻫﯽ ﮐﻢ در ﭘﯽ ﻋﻤﻞ ﭼﺮا، ﺧﺎك-داﻧﻪﺳﺎزي و درﺻﺪ ﺧﺎكداﻧﻪﻫﺎي ﺑﺰرﮔﺘﺮ از 2 ﻣﯿﻠﯽﻣﺘﺮ ﮐﻤﯽ داﺷﺘﻪ؛ اﻧﺪازه ﺧﺎكداﻧﻪﻫﺎي 0/053-0/5 ﻣﯿﻠﯽﻣﺘﺮ در ﺧﺎك ﺗﯿﭗﻫﺎي ﻣﺬﮐﻮر ﺑﯿﺸﺘﺮ از دﯾﮕﺮ اﻧﺪازه ﺧﺎكداﻧﻪﻫﺎ ﺑﻮد. ﮐﺮﺑﻮﻫﯿﺪرات ﮐﻞ و اﻧﺪازه ﺧﺎكداﻧﻪﻫﺎي 0/053-0/5 ﻣﯿﻠﯽﻣﺘﺮ ﺷﺎﺧﺺﻫﺎي ﻗﺎﺑﻞ اﻋﺘﻤﺎد ﮐﯿﻔﯿﺖ ﺧﺎك ﻫﺴﺘﻨﺪ ﮐﻪ ﺗﻐﯿﯿﺮات ﮐﺎرﺑﺮي و ﭘﻮﺷﺶ ﮔﯿﺎﻫﯽ را ﻧﺸﺎن ﻣﯽدﻫﻨﺪ.

The combined effects of biochemical composition and amount of plant residues returned to soils affect stability of aggregation and the rate of aggregate turnover. To investigate the influence of vegetation type on aggregate size distribution, five vegetation types including rainfed wheat (RW), grasses (G), Astragallus–Bromus (A-B), Astragallus–Lactuca (A-L) and Astragallus–Artemisia (A-A) were studied under similar environmental conditions in terms of parent material and slope aspect in Gonbad watershed, Hamadan. Total organic carbon (TOC), soil carbohydrates (Ch), mean weighted diameter (MWD), size distribution of water-stable aggregates (AS) and aggregate carbon (AC) were measured in surface (0-15 cm) soils. The amounts of TOC, Ch, MWD and AC (present in all aggregate size fractions) were significantly greater in soils under A-B and A-A than the soils of other vegetation covers, while the lowest values were observed in soils under RW and G. The highest AS>2 mm and lowest AS 2 mm were lower in soils under A-L, G and RW compared to other aggregate sizes. A-B and A-A vegetation types had greater canopy, annual production, plant diversity and litter content compared to other vegetation types.Frequent soil ploughing in RW site andlow plant diversity and canopy cover in A-L and G sites contributed to reduced soil aggregation and lower content of coarse aggregates;AS in 0.5-0.053 (mm) fraction in soils of aforementioned vegetation types was greater than other aggregate sizes. It was concluded that Ch and 0.5-0.053 (mm) aggregate size fraction might be reliable soil quality indicators that reflected land use and vegetation type changes.