A modification of the leaf-bags method to assess spring ecosystem functioning: benthic invertebrates and leaf-litter breakdown in Vera Spring (Central Italy)

The evaluation of leaf detritus processing (decomposition and breakdown) is one of the most simple and cost-effective method to assess the functional characteristics of freshwater ecosystems. However, in comparison with other freshwater habitats, information on leaf litter breakdown in spring ecosystems is still scarce and fragmentary. In this paper, we present results of the first application of a variant of the leaf-bags method to assess structure of macroinvertebrate assemblages and leaf-litter breakdown in a Central Apennines (Italy) cold spring which was investigated from July 2016 to October 2016. Notwithstanding the stable conditions of almost all hydrological and physico-chemical parameters, we found significant temporal differences in (i) % of mass loss of poplar leaves (ii) number of Ephemeroptera, Plecoptera and Trichoptera taxa, (iii) shredder and predator densities. We demonstrate that detritus processing in cold springs may be faster than or as fast as in warmer streams/rivers. Shredders activity and biocoenotic interactions, rather than temperature and nutrients load, were the main drivers of the process. A routine application of the modified leaf-bags may contribute to expand our knowledge on detritus processing in cold springs and may help to predict impacts of climate warming on freshwater ecosystem functioning.

LAJU DEKOMPOSISI BAHAN ORGANIK DAN PRODUKSI INVERTEBRATA AIR DI SUAKA PERIKANAN TELUK RASAU, SUMATERA SELATAN

Pembukaan lahan di lahan banjiran untuk berbagai kepentingan, mempengaruhi morfologi, siklus hidrologi, dan karakteristik fisika kimia air seperti input dan dekomposisi bahan organik yang akhirnya akan mempengaruhi struktur organisme invertebrata air dan produksi ikan di rawa banjiran. Penelitian ini bersifat percobaan lapangan yang bertujuan untuk mengetahui laju dekomposisi bahan organik dan produksi invertebrata air dilakukan di tiga stasiun di Teluk Rasau, Sumatera Selatan pada bulan September sampai Nopember 2009. Laju dekomposisi bahan organik dan produksi invertebrata air dilakukan dengan metode jaring kantong (litter bag) berukuran 20x10 cm dengan ukuran mata jaring2 mm. Daun dari tumbuhan yang dominan yaitu pohon serpang (Caesalpina sappan) yang hampir gugur dikumpulkan dan ditimbang bobot keringnya, dan 5 g dari daun tersebut dimasukan ke dalam jaring kantong. Pada masing-masing (stasiun) percobaan diletakan 40 kantong jaring dengan posisi20 kantong diletakan pada kedalaman air 0 m (perbatasan air dan darat) dan 20 kantong pada kedalaman 75 cm. Kantong diikatkan tiang kayu dan ditenggelamkan dengan menggunakanpemberat. Pengukuran jumlah bahan organik yang terdekomposisi dan produksi makrozoobenthos dilakukan pada minggu ke-2, 4, 6, 8, dan 10, dengan cara mengangkat empat kantong plastik pada masing-masing kedalaman. Contoh air diambil pada kedalaman 1 m dari dasar perairan denganmenggunakan kemmerer water sampler. Sebagian contoh dianalisis di lapangan (kedalaman air, kecerahan, suhu, pH, dan oksigen terlarut) dan sebagian lagi akan dianalisis di laboratorium (dissolved organic carbon, nitrogen total, dan fosfor total. Persentase serasah daun serpang yang terdekomposisiselama 10 minggu pada kisaran 40-55%. Koefisien laju dekomposisi serasah daun serpang pada muara Teluk Rasau yang berhubungan dengan Sungai Lempuing pada kedalaman 0 cm (k=0,1586) lebih rendah dari stasiun lainnya baik pada kedalaman 0 cm ataupun 75 cm (k=0,2076-0,2566). Produksi makrozobenthos di muara Teluk Rasau yang berhubungan dengan Sungai Lempuing baik pada kedalaman 0 cm ataupun 75 cm (9,25; 117,25 mg bobot kering/m2) secara nyata lebih rendah dari stasiun lainnya (17,75-22,08 mg bobot kering/m2; 260-807 mg bobot kering/m2). Kedalaman air, suhu, alkalinitas total, dan unsur hara sangat mempengaruhi laju dekomposisi serasah dan produksi makrozoobenthos. Clearance of floodplain area for multiple purposes influence morphology, hidrological cycle, and physical and chemical characteristics of water such as input and decomposition of organic matter in the waters. It finally affect the structure community of invertebrate and fish production. Experimental study in order to know decomposition rate of organic matter and aquatic invertebrate production was conducted at three sampling sites located in Teluk Rasau Fisheries Reserve Area of South Sumatera province from September to November 2009. Decomposition rate and invertebrate production was run with litter bag method. Leaf bags were constructed by placing 5 g of Caesalpina sappan in plastic with the size of 20x10 cm and mesh bags (mesh size 2 mm). Leaves were collected before abscission, air dried and stored. In each sampling sites, 20 litter bags were filled with dry leaves and placed on the sediment at water depth 0 m (transition between land and water), and another 20 litter bags were placed on the sediment at 0.75 m water depth. The litter bags were tied to the wood stake and anchored to the bottom. The leaf bags were tied together with a weighted rope and attached to a tree. Four replicate samples were removed after 2 days, to measure the leaching process, and then after 4, 6, 8, and 10 weeks for organic matter decomposition rate and invertebrate production measurement.The bags were cut from the rope and immediately placed in sealed plastic bags and returned to the laboratory. In the laboratory, the leaves were rinsed and separated from the invertebrate. The leaves were sorted by genus, dried at 50°C and weighed. invertebrate were counted and identified to different taxonomic levels. Physical and chemical water quality parameters were measured both in and exsitu by collecting water samples with kemmmerer water sampler at 1 m depth above the bottom. Parameters measured insitu were the water depth, transparency, temperature, pH value, dissolved oxygen, while, dissolved organic carbon, total nitrogen, and total phosphorus were analyzed in the laboratory. Results indicated that decomposition rate of Caesalpina sappan leaves for 10 weeks was in the range of 40-55%. The decomposition rate coefficient in the inlet of Teluk Rasau connevting to Lempuing River at depth 0 cm ((k=0.1586) was less than that in other sampling sites both at depth ocm and 75 cm (k=0.2076-0.2566). Macrozoobenthos production in the inlet of Teluk Rasau connecting to Lempuing River at depth 0 and 75 cm (9.25; 117.25 mg dry weight/m2) were less than that in other sampling sites (17.75-22.08 mg dry weight/m2; 260-807 mg dry weight/m2). Decomposition rate and invertebrate production of Caesalpina sappan were affected by water depth, temperature, total alkalinity, and nutrient.

Bagworm bags as portable armour against invertebrate predators

Some animals have evolved the use of environmental materials as “portable armour” against natural enemies. Portable bags that bagworm larvae (Lepidoptera: Psychidae) construct using their own silk and plant parts are generally believed to play an important role as a physical barrier against natural enemies. However, no experimental studies have tested the importance of bags as portable armour against predators. To clarify the defensive function, I studied the bagwormEumeta minusculaand a potential predatorCalosoma maximoviczi(Coleoptera: Carabidae). Under laboratory conditions, all bagworm larvae were attacked by carabid adults, but successfully defended themselves against the predators’ mandibles using their own bags. The portable bags, which are composed mainly of host plant twigs, may function as a physical barrier against predator mandibles. To test this hypothesis, I removed the twig bags and replaced some with herb leaf bags; all bag-removed larvae were easily caught and predated by carabids, while all bag-replaced larvae could successfully defend themselves against carabid attacks. Therefore, various types of portable bags can protect bagworm larvae from carabid attacks. This is the first study to test the defensive function of bagworm portable bags against invertebrate predators.

Leaf quality influences invertebrate colonization and drift in a temperate rainforest stream

Changes in riparian forest composition and diversity, such as plantations of exotic species, may alter resource quality, detritivore assemblages, and litter breakdown rates in streams. We hypothesized that different litter resources may influence colonization and drift of invertebrates inhabiting small, temperate rainforest streams in southwestern British Columbia, Canada. Leaves of different quality and origin were incubated in stream-side channels to test this hypothesis. The sequence of leaf decomposition rates was as follows: alder > alder + cedar > cedar ≥ eucalyptus. Cedar litter decayed faster when mixed with alder than when alone. Invertebrates colonizing leaf bags were predominantly collector–gatherers and shredders, particularly on alder leaves. Drift density varied over the incubation period and seemed to be controlled by leaf quality, since there were more individuals drifting from channels with alder leaves than from channels with cedar or eucalyptus. However, we observed different species-specific invertebrate responses controlled by leaf traits, particularly by numerically dominant chironomid species. Indeed, invertebrate drift from channels incubated with alder bags was mostly due to pupation and emergence of orthoclad midges, whereas this was not observed in the other channels. This differential response in colonization and drift has the potential to modify the transfer rates of organic matter to higher trophic levels and thus ecosystem functioning.

Decomposition of native leaf litter by aquatic hyphomycetes in an alpine stream

Despite the recognised significance of hyphomycetes in the degradation of leaf litter in streams, few studies have been carried out in alpine environments and none in Australian alpine streams. We hypothesised that the fungal communities responsible for leaf decomposition would change over immersion time, and would respond differently at different sites and on different types of vegetation. Leaf bags containing Epacris glacialis (F. Muell.), Eucalyptus pauciflora (Sieber ex. Spreng) and Eucalyptus delegatensis (R.T. Baker) were deployed at different sites in a stream in the Victorian Alpine National Park, south-eastern Australia. Leaf colonisation was delayed for 2 weeks and decay constants for E. pauciflora and E. delegatensis were 0.004–0.005 and 0.006 respectively. Maximum fungal biomass on leaves was similar to that in previous published studies, whereas sporulation rates were two or three orders of magnitude lower, indicating a reduced reproductive effort. Sporulation and DNA-based studies combined showed that fungal communities on the decomposing leaf material changed over time and exhibited significant preferences for leaf type and study site. We have shown that aquatic hyphomycetes can degrade physically tough leaves of Australian alpine plant species, potentially contributing to pathways for particulate carbon to enter alpine-stream food webs.

Nutrient addition does not enhance leaf decomposition in a Southeastern Brazilian stream (Espinhaço mountain range)

A decomposition experiment using eucalyptus leaves was carried out in a Southeastern Brazilian mountain stream located at the transition between the Cerrado and the Atlantic Forest to test whether nutrient addition increases microbial and invertebrate colonisation and accelerates breakdown rates. The results show that none of the tested variables was significantly affected by nutrient addition, despite the average increase in ATP concentrations and invertebrate colonisation observed in the fertilised leaf bags. This could mean that breakdown in the stream was already at its maximum due to the relatively high water temperature and nutrient content, or that the breakdown rate of eucalyptus leaves was too fast to allow the detection of any effects of nutrient addition. Breakdown rates of eucalyptus leaves were much faster than the values reported in literature for most species in Brazilian Cerrado streams, suggesting that the replacement of the natural vegetation by eucalyptus may affect nutrient dynamics in the region.